Everyone is trying to sell you unlimited data again. Some options are better than others, though.

It was only a few years ago that most of the big US carriers were trying to tell us we didn't need unlimited data, Verizon was even running ads to that effect a few weeks ago. Now, here we are in the midst of a new battle for the best "unlimited" data plan among the top four carriers. Of course, there are a surprising number of limits in these plans.

Carriers start throttling your usage at different points, and not all plans include full HD video by default. There are also some differences in tethering support. Let's see how they stack up.

Verizon Unlimited

It was Verizon that kicked off the latest round of interest in unlimited plans after it brought back the option with much fanfare a few weeks ago. Verizon has allowed users to keep their grandfathered unlimited plans from years ago, but the throttling kicks in faster and more aggressively than with the new plan.

Cost: Verizon's plan start at $80 for unlimited data on a single line. Two lines is $140, three is $162, and four is $180. The 4-line pricing is the best overall deal on a cost per-line basis. These prices all assume you get the $5 per month discount for auto-pay. Phone payments are extra, of course. The marketing on this is very straightforward.

Tethering: Verizon's unlimited plan includes 10GB of LTE tethering. After you've used your allotment, you can keep tethering at 3G speeds.

Throttling: Verizon will deprioritize your connection after you've used 22GB in a single billing cycle. That doesn't mean you'll instantly see your speeds decrease, but your speeds will probably slow when towers are congested. Verizon does throttle video, but at a poorly explained "HD" bitrate. You should be able to stream 1080p resolution fine. No other media types are throttled.

T-Mobile ONE

T-Mobile's unlimited ONE plan has been around for a while, but it was not a good deal at all with all the crazy limits it imposed. T-Mobile lightened up dramatically in response to Verizon. ONE is the only plan T-Mobile offers, which is a bummer if you're looking to go cheap. T-Mobile has had a few different unlimited plans in the past, most of which were better deals than ONE. There are a number of annoying limits still.

Cost: T-Mobile offers ONE at $70 per month for a single line, but that includes all taxes and fees. Two lines are $100, three are $140, and four are $160. So, T-Mobile is a few bucks cheaper at each tier than Verizon. You can add a Plus option for $5 per month that includes unlimited Gogo in-flight WiFi or a $25 international plan with unlimited LTE tethering and free calls to a bunch of countries. None of this includes phone payments if you've financed a phone through T-Mobile.

Tethering: The default ONE plan comes with 10GB of LTE tethering now. After that, you're down to 3G speeds. The international add-on removes that 10GB limit.

Throttling: T-Mobile says it throttles the top 3% of users who consume about 28GB in a single month. That means you will probably see your speeds dip during times of heavy usage once you hit the limit. As for video, T-Mobile ONE defaults to be throttled at 480p (i.e. Binge On). The video data doesn't count against you, but that doesn't matter much for unlimited plans. You can disable Binge On, which was not possible on ONE previously. There were lame HD passes that had to be enabled every day. Now it's just a one-time change.

Sprint Unlimited

Like T-Mobile, Sprint has been offering unlimited plans for a while, but it's stepping up its efforts to compete with Verizon. However, Sprint's current offering has perhaps the most caveats. On the plus side, it has a number of normal capped plans that you can get instead.

Cost: Sprint's current unlimited plan offers a single line of unlimited data for $50, two lines for $90, and it's the same for three and four lines. That's a good deal, but it's not a permanent price. This is only a promo that's valid through March of next year. At that time, the price goes up to $60, $100, $130, and $160. This pricing assumes a $5 monthly auto-pay credit, and phone payments are extra, of course.

Tethering: Sprint only offers 10GB of LTE tethering on its unlimited plan, the same as other unlimited plans. After the 10GB is gone, you're down to 2G speeds. That's essentially unusable, and T-Mobile and Verizon are offering 3G overage speeds now.

Throttling: Lines that have used more than 23GB in a month might be slowed on Sprint's network. That's in-line with other carriers. When that price break goes away, you also get a downgrade in service. Right now, the plan includes unthrottled HD video, 1.5Mbps for music, and 8Mbps for games. That'll go down to 480p video, 500Kbps music, and 2Mbps for games next year. That's all very, very dumb.

AT&T Unlimited

Before this whole unlimited battle started, AT&T had an unlimited plan you probably couldn't buy. I don't mean those grandfathered plans that AT&T has been throttling more and more over the years. You could get an unlimited plan from AT&T for $100 per month if you had DirecTV. AT&T's first swing at being competitive was to remove the DirecTV requirement. That was a bad deal (it didn't even have tethering), so AT&T has just revamped its plan.

Cost: There are now two tiers of unlimited on AT&T. The Unlimited Plus plan costs $90 for the first line, $145 for two, $165 for three, and $185 for four. So, a little more than Verizon. The stripped down Unlimited Choice plan is priced at $60, $115, $135, and $155. This pricing includes a $5-10 auto-pay credit.

Tethering: Only the Plus plan has tethering. It's 10GB of LTE, then slows to 2G (128Kbps). That's too slow to get much done.

Throttling: After 22GB of data, AT&T may throttle its unlimited plans during times of heavy usage. Nothing unusual there. What is unusual is the way it throttles the Plus and Choice plans differently. The Plus plan has full resolution video after you disable AT&T's Stream Saver "feature." Choice is locked to 480p video (about 1.5Mbps). Worse, Choice plans are stuck with a maximum speed of 3Mbps for all other on-device data—basically 3G.

Is there a winner?

Oddly, Verizon's unlimited plan seems to be the most appealing based on coverage and simplicity. Verizon was complaining about unlimited plans very recently, but here we are. T-Mobile is a little cheaper, but you have to mess around with the Binge On toggle, and there are two extra add-ons for unlimited. Either one is a good choice, though.

AT&T is fine if you really need to be on AT&T for some reason, but it's not really competitive on price or features. Steer clear of that Unlimited Choice plan, though. Then there's Sprint, which is being extremely disingenuous with its offering. The pricing is a promo that will expire next year and get vastly more expensive, and the service will get slower. By that time, you might only be halfway through paying off the phone you bought from Sprint.