The Sony Z5 smartphone. Credit:Peter Wells There are a few small differences between the Z5 and Compact. The Z5 Compact's 4.6 inch screen is 720p, while the Z5's 5.2 inch screen is full HD, at 1080p. I doubt most people will notice the difference in resolution; both screens are more than good enough for my eyes. The Z5 has 3GB of RAM, the Compact has 2. But again, most users will never notice. And the Compact is $150 cheaper than the Z5. But everything else, everything Sony is prioritising, is shared between the handsets. Both have the same impressive camera, a full two days' battery, a fast and accurate fingerprint reader, and support Sony's Remote Play. It's fantastic to see Sony continues to make the Compact Z5 just as powerful as the larger phone. First, that camera: Sony's optics power the best cameras in the best smartphones today, so it should be no surprise the camera in the Xperia is fantastic. The 23 megapixel camera performs well in most situations, the Intelligent Auto settings accurately detect the scene you're shooting and adjust to portrait, landscape, low light, and sport. Photos from the Z5 were sharp, well balanced, and were easily adjustable for manual photography. The one area where I questioned the camera's automatic settings were in very low light. The Xperia created dark, saturated images, where the iPhone 6s would go for a lighter, desaturated look. Both look great, but I think I prefer the iPhone's auto in low light.

The Z5 Compact has all the power of its larger siblings but in a small frame. Like the Z5, it has a frosted glass back. Credit:Peter Wells Sony touted the Xperia camera's autofocus as fastest in the business. They measure this in milliseconds, so I cannot verify the claim. But unfortunately most users will notice another, slower feature of the phone: in my testing the camera app can take up to 10 seconds to load – frustratingly slow. Once the camera app is up and running, snapping is fast. But you'd better have the camera ready for candid shots.

Reviewing those hefty 23 megapixel pictures, swapping from the camera app to the gallery, is also painfully slow. Hopefully this is down to some launch day buggy software, but more on that later. Next, that battery. In my testing, I hammered the battery – taking hundreds of photos, streaming podcasts over Bluetooth, using Google Maps, and for fun, even making an old fashioned phone call. After a full day of heavy use, taking the tiny Z5 Compact off the charger at 7am, I'd still have around 30 per cent battery at midnight. After a day of moderate usage, I had just over 60 per cent when I went to bed. The battery is fantastic, which is especially impressive for the Z5 Compact. The Xperia Z5 and Compact are quite boxy when compared to the gorgeous curves of the Samsung Galaxy S6 edge, or the rounded edges of the iPhone 6s. That's not to say the phones are unattractive; I think both sizes look great. It's just the frosted glass back and glossy front are more classy than flashy, like an upmarket sedan compared to a sports car. Both sizes are available in black and white, with the larger model available in green and gold, while the Compact comes in yellow and pink. For me, the yellow Compact is the pick of the bunch; it looks fantastic from any angle, and so different to everything else on the market.

The Compact is a little fatter than the regular size Z5. Here's where the priority of battery life trumps design, and I can't help but wish other smartphone makers would add a few extra millimetres of thickness to their phones for a few hours more battery. The sides of the Xperias are a smooth plastic, making the phone feel as though it's wrapped in a wafer thin, bumper-style case. This makes the Xperia one of the grippiest flagships on the market, a welcome change after using recent smartphones with all the grip of a bar of soap. I'm glad the Xperia range have joined other flagship phones in getting a fingerprint reader. Sony have incorporated their fingerprint reader into the unlock button on the side of the device. It feels great on the side — unlocking the phone feels as natural as holding the phone. The fingerprint reader is fast, and more importantly accurate. I've unlocked the phone countless times in the last week, using the phone as my daily driver, and had just one failure to unlock. My password manager of choice, Lastpass, and my banking app from Commbank do not yet supporting the fingerprint reader. I hope both will support the Xperia soon. If they don't, Android 6.0 (Marshmallow) includes system-wide application programming interface (APIs) for fingerprint readers which should allow for easier integration of third party software in the future. The Xperia range is marketed as waterproof – I'd be too nervous to use one underwater, but I'd happily use the phone in the rain, and that's enough for me.

Unfortunately, one priority all smartphone manufacturers share is hitting their marketed release date, even if the software is not completely ready for primetime. The Sony Xperia software has felt quite buggy in this opening week. Using Google's launcher and keyboard made the Xperia screen jump around and register taps late, not at all, or register three taps instead of one. The issue seemed to be some kind of memory leak – locking and unlocking the phone would fix it – suggesting the issue could easily be fixed with a software update. After much troubleshooting, I returned to Sony's own launcher and keyboard – both are fine by the way, the Sony keyboard is actually one of the better built-in Android keyboards I've used – and the issues disappeared for me. Other reviewers I've spoken to are still experiencing the odd rough edges in the software. The Xperias are not the first handsets I've used this year to ship with buggy software, and I'm sure these teething issues will be fixed with a software update, but it's a shame my first full day with this phone was spent fighting with the screen. If you're nervous, wait a few more weeks – I'll be sticking with the Xperia Z5 Compact for a while, so I'll report back on Twitter any updates the phone receives. Opening week bugs aside, the Z5 update to the Xperia family is a solid one. The fingerprint reader adds security and convenience, and the overall design of the phone looks a lot better than last years Z3 lineup.

Both phones deliver on the promise of a great camera and exceptional battery life. And if you're one of those seemingly rare people who want a smartphone smaller than 5 inches, something you can easily navigate one handed, you won't find a better handset than the Xperia Z5 Compact. The Z5 Compact will be available outright from Sony or JB Hi-Fi this week at a recommended retail price of $849. The Z5 will be available from the same stores for $999. When it launches in November, the Z5 Premium will cost $1199 outright in chrome, black or gold.