If you are going to get an Android phone any time soon, this is it.
Let's get this out of the way: These things are fast. They haul all kinds of ass, thanks to a 1.2GHz dual-core Exynos processor and 1GB of RAM in its guts. I did everything I could to try to make Galaxy S II stutter and I failed, miserably. Like really, that's the most major advancement in this phone. It's super-duper fast. And man that screeen. Gorgeous. Bright, clear, nice colors, responsive touchscreen. Super AMOLED Plus really delivers on just about every metric.
There's a few differences between the three models on each carrier. Most significantly, AT&T's has a 4.3-inch screen, while Sprint and T-Mobile's phones are 4.52-inch monsters. AT&T's felt the best—and I've got pretty damn big hands. But the 4.3 was just less of a reach for my fingers, and the screen seemed plenty big for anything I might be trying to read.
The rear camera, both for still and video, is excellent. It responded quickly, did well in low light, and video playback was smoother than Morgan Freeman's voice.
They're all super light and super thin, and that's nice, but they're also super-plasticky. I'd rather they had some sturdy hardcore metal backs, so I didn't feel like they'd break if I dropped them. And despite the baller 8-megapixel, 1080p-shooting camera, none of these phones have a dedicated camera button. Why would you put an awesome camera on your phone and then not have a button for it?
I've gone on record as not being fan of Samsung's TouchWiz UI, but after playing with TouchWiz 4.0—I'm still not. I feel like Chris Crocker screaming, "Leave Britney alone!" except, substitute "Android" for "Britney". It's fast now, but I can't help but think it'd be even faster without the extra bulk. That said, TouchWiz 4.0 is more palatable than its previous incarnation. It's important to note that phones with custom skins like TouchWiz (and Sense and MotoBlur) have traditionally gotten updates slower than phones that run stock Android. We hope that Samsung will somehow break that trend.
Aside from the minute differences in screen size the only other way the carriers differentiate here is by loading it with their own custom junk. Sprint had no less than seven custom apps (Sprint Music, Sprint Zone, etc.) and AT&T had a good handful, too (AT&T Navigator, AT&T Code Scanner, etc.). This is bloatware.
From this quick hands on, it seems like the Galaxy S II is fastest smartphone you can get stateside. I'll have to do some additional torture testing to confirm that, but these things really fly. And while I don't like the plastic body, they're light, thin, fast, and pretty. Overall, if you're been waiting for a new Android phone to drool over, these fit the bill nicely. Though, with the rumored Nexus Prime (or Droid Prime, depending who you ask) coming within the next few months and bearing Android 4.0, these guys will have some stiff competition very soon.