iOS 5, Android 4 "Ice Cream Sandwich," Windows Phone 7.5 "Mango," and BlackBerry OS 7 were all released in the past few months, each promising to advance the iPhone, Android smartphones, Windows Phones, and BlackBerrys respectively to the head of the mobile pack. But only one can be the best.

InfoWorld has tested each of the major mobile OSes on the flagship devices for each OS to see what the best smartphone is for business and professional users. The answer is without a doubt the iPhone 4S, thanks to iOS 5, the Apple ecosystem, the smartphone's solid hardware, and the new Siri voice-controlled "intelligent" assistant. But as good as the iPhone 4S is, it does not beat the competition in every respect, showing it has room for improvement and that Apple doesn't excel at every aspect of modern mobile computing.

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For the deep details of each of the major devices, read our full reviews, as this comparison focuses on the highlights and lowlights of each platform's flagship smartphone:

You can also calculate personalized scores for all of these devices by entering your own weightings for each review category in InfoWorld's smartphone calculator.

Deathmatch: Hardware

The Galaxy Nexus's 4.65-inch Super AMOLED screen gets the oohs and ahhs -- the same phenomenon you see at a Best Buy as people drool over the 70-inch HDTVs. But the Samsung Focus S's 4.3-inch screen boasts the best size of the bunch -- it makes the iPhone 4S's 3.5-inch screen feel cramped. The Galaxy Nexus's support for 4G cellular networks places it as the winner in connectivity, though 4G penetration is quite low; this capability matters little now, but it will become more relevant as the year progresses.

But the iPhone 4S wins on every other hardware count. It has a very fast processor, wired and wireless video-out capabilities, low-power Bluetooth, a high-density Retina display, the highest-quality rear camera, strong battery life, a worldphone-capable 3G radio, and a high-quality steel and glass bezel. (The BlackBerry 9900's bezel is of equally high quality.)

The lowlights of the hardware for today's flagship smartphones are the puny 8GB of RAM in the BlackBerry Bold, the flimsy, tacky back cover of the Galaxy Nexus, and the BlackBerry Bold's poorly placed camera button.

Deathmatch: Business connectivity

The iPhone has the best, most desktoplike business connectivity of the bunch, with the best support for Microsoft Exchange and IMAP email, the richest message capabilities, and the easiest-to-use calendar. But competitors exceed the iPhone's iOS 5 in some areas. For example, the Galaxy Nexus's Android 4 has a better mechanism for navigating multiple accounts, and the BlackBerry is unchallenged in its support for sophisticated repeating-event patterns.

Lowlights include iOS's inability to work natively with zipped attachments, iOS's inability to create groups of contacts, the BlackBerry's awkward time-stamping of messages received when offline, and iOS's poor integration of social networking.

Deathmatch: Application support

This category is one where the iPhone 4S shines the brightest. Not only does the App Store have a huge array of useful, richly capable apps (in addition to the junk found in all app stores), but the entire Apple ecosystem -- AirPlay, iCloud, and iTunes -- makes it oh-so-easy to bring an iPhone into your whole computing context, especially if you use a Mac. The iPhone also has the best control over location information usage, providing the most user privacy of the bunch. It also offers more useful core apps than the rest, such as with its Notes and Reminders apps, and has one-upped Android's notifications capability with a better approach.

The iPhone 4S takes all these iOS 5 advantages and adds the Siri voice-based personal assistant to the mix. Siri is simply amazing, despite its beta status. You can actually talk to your iPhone and have it understand much of what you are asking and saying. Its voice recognition, both for dictation and interactive queries, is unmatched by the other voice-capable platform, Android, whose once-heralded voice search and dictation features suddenly feel primitive. Windows Phone 7.5's voice search is the least accurate, and it offers (inaccurate) dictation only for sending text messages.

Apple has consistently made its OS upgrades work with devices produced in the previous two years, ensuring both a more coherent ecosystem and rewarding customers' investments in its platform. By contrast, Android devices are rarely upgraded to a new OS, even those that come out mere months before an OS upgrade, as has become painfully clear in Android 4's recent release. Likewise, RIM orphaned existing BlackBerry users when its new models came out last summer, and the company says these new models won't run the BlackBerry 10 OS expected late this year. Would-be Android and BlackBerry buyers thus should think twice.

The other lowlights for application support are the BlackBerry's poor app catalog and generally clunky core apps, Windows Phone's primitive (and embarrassing) Office apps, Windows Phone's very poor voice recognition in its voice-command interface, and Google's malware-laden Android Market. And darts to Apple and RIM for promoting messaging and, in the case of iOS, videoconferencing apps that work within only their own platforms.

Deathmatch: Web and Internet

If HTML5 support matters in the websites you access, no mobile browser works with as many aspects of the still-evolving standard as Apple's Safari. In second place is, surprisingly, BlackBerry OS. Android 4 is in third place, and Windows Phone is far behind. Safari also does better than the other browsers when accessing AJAX-oriented websites, though it's not as yet up to the level of desktop browsers.

Safari also has two very handy browser capabilities that keep it ahead of the pack: the Reading List feature for temporary bookmarks and the Reader feature for simplified Web page display. But Safari isn't always the best mobile browser; Android 4's Chrome browser and Windows Phone's Internet Explorer provide a handy option to request a desktop page rather than the not-always-optimal "mobile optimized" page many sites serve up to smartphones.

There are just a few lowlights on this category. One is Android 4's inability to properly render some Web pages or to identify itself as either a smartphone or tablet to many websites. Another is iOS's poor support for social network sharing of Web pages. Finally, there's Windows Phone's embarrassingly poor HTML5 compatibility.

Deathmatch: Usability

The iPhone's iOS has the most consistent and intuitive user interface of the bunch, augmented by the richest set of gestures and accessibility controls. As an example of that user-friendly approach, when you select text in iOS, the area you are tapping and holding is magnified, so you can more easily see where you are putting your text cursor. And there are often quick-access shortcuts for frequent actions, such as the quick flick to reveal the Delete button on emails in the message list. The ability to set custom vibrations, not just ringtones, is another example of thinking about the user in multiple contexts. Then there's the ability to create your own text shortcuts that work everywhere.

Siri offers iPhone 4S users a whole new dimension of usability beyond what iOS 5 offers all other iPhone and iPad users.

Still, Windows Phone's slick UI is intuitive, though its scrolling approach does get tedious once you have more than a few of whatever -- apps, contacts, messages -- to navigate. Android 4's resizable widgets are very handy for getting quick but useful detail on your social networking feeds, email, and other such frequently updated information. iOS's notification facility only partially satisfies that need.

When it comes to lowlights, the lowest of the low is the overall BlackBerry experience, a painful mishmash of DOS-like screens, early-Windows-like menus, confusingly obscure icons, and partial use of touch. A close second is Windows Phone's unreadable text, caused by a deadly combination of small size and low-contrast colors.

Deathmatch: Security and management

The BlackBerry has the greatest degree of security and management, but it requires the use of the extra-cost BlackBerry Enterprise Server (BES), and many of its security settings require IT intervention. It's a Pyrrhic victory. Without BES, the BlackBerry is even less secure and manageable than Windows Phone 7, though BlackBerry OS supports VPNs, whereas Windows Phone 7 does not.

iOS comes in second after the BlackBerry, with core security capabilities manageable directly from Microsoft Exchange and extended controls manageable through mobile device management (MDM) tools. iOS 5's new support for the S/MIME email security protocol and other MDM extensions improve on the iOS 4 capabilities that finally made the iPhone acceptable to many IT organizations. Android 4 has improved significantly in this area, leaving Windows Phone 7 the only mobile OS that can't have at least moderate security and management applied to it.

Looking forward to 2012 improvements

It's clear that the iPhone 4S is the best smartphone overall, at least today. But there's room for improvement in the iPhone, as there is in the other mobile platforms.

A crying need for all is printing capability. Although iOS has a printing facility built in, it works with only a handful of AirPrint-compatible printers, and the recent iOS 5.01 update broke several printing utilities that exploited a hole (now closed) in iOS that allowed wireless printing to other devices. What's sad is that even with these severe constraints, iOS has the best printing support of the bunch.

As smartphones grow more capable, screen mirroring and the ability to use input devices -- keyboards and mice -- will be more useful as people start to use them as surrogate PCs, at least occasionally. iOS 5 (on the iPhone 4S and iPad 2) and Android 4 already support screen mirroring over a cable, and iOS 5 supports it through the AirPlay protocol currently available only on the Apple TV. There are ways to connect USB keyboards to iPhones (through the Apple Camera Connection Kit, if the keyboard's power usage is low enough), and Motorola Mobility's docks provide HDMI and USB connectivity to its various "business-capable" Android smartphones. But it'd be great if you didn't have to look for hacks or be limited to just a few smartphone models to use them as on-the-go PCs.

Support for 4G networks will be increasingly important as the coverage spreads across greater swaths of the country. Look to Verizon Wireless first for such availability, followed by Sprint. Beware AT&T's and T-Mobile's 4G claims; they misuse the label for marketing reasons to refer to their fast-3G networks, though AT&T is finally deploying real 4G (meaning LTE networks). I expect 2012's "iPhone 5" to support LTE, and Android devices such as the Galaxy Nexus already do so.

We may also see near-field communication (NFC) technology widely deployed, though right now there's not much you can do with this short-range wireless technology. A few of RIM's BlackBerry OS 7 devices support it, but only a few carriers have enabled it and most payment operators are still deciding whether to support it; the Galaxy Nexus and other Android devices ship with it, and Android 4 lets you use it to share URLs, contact information, and the like if you "bump" with another NFC-equipped Android 4 device. NFC can also be used to pay parking meters and interact with other payment terminals. The big questions are whether NFC will remain an "only within the platform" technology and whether Apple will join the NFC party or use low-power Bluetooth (already in the iPhone 4S) instead.

Android 4 made a good start to improving the interface, but it's still inconsistent. It has even introduced some new metaphors and inconsistently implemented them, so it has a ways to go to be a polished OS. Windows Phone 7 is proficient but can do little beyond social networking, and it's unclear whether Microsoft will try to make it a full-on platform like iOS or Android. Then there's BlackBerry OS, which is being replaced later this year with a new OS -- assuming RIM can finish the job, given its many delays and declining revenues.

I suspect through all this, the iPhone 4S and the forthcoming "iPhone 5" will remain the best smartphone.

Also on InfoWorld.com:

This article, "Smartphone face-off: iOS 5 vs. Android 4 vs. Windows Phone 7.5 vs. BlackBerry OS 7," was originally published at InfoWorld.com. Follow the latest developments in mobile computing, read Galen Gruman's Mobile Edge blog at InfoWorld.com, follow Galen's mobile musings on Twitter, and follow InfoWorld on Twitter.