I prefer Samsung Galaxy S3 unlocked, I bought mine here:
Phone works very well with very good battery life. With moderate to heavy use I can get over 24 hours. Going all day is not an issue.
Yes, it is only 3G in order to own the quad core. The U.S. 4G dual cores will be out soon.
On WiFi I can download large Flash intensive pages in 2-3 seconds. Faster than anything I have seen. On 3G it appears to be as fast as Sprint Epic 4G Touch (in 3G mode). Maybe the Sprint Galaxy S2 is faster in 4G mode but I haven't tested it against my other phone. The AT&T 3G is reaching spots where Sprint 3G and 4G were not getting. And as a disclaimer, I am not a fan of AT&T. Reception seems very good. No dropped calls and it is perfect inside my house (which has been very difficult for almost every other phone I have owned). I have not tested reception extensively.
I pay about $140 a month with no contract for service. That is unlimited minutes, unlimited texts and 5GB/mo of data. A bit pricey.
There are a couple of things I dislike about the operating system, but it is overwhelmingly an upgrade from Android 2.3.6. The camera is not quite as fantastic as I was hoping for. But maybe that is because the S2 camera is so good, it was hard to improve on it. I am talking about picture quality, not features. The picture quality of my S2 seems better.
The notification system is all or none. You get beeped for a text, but also for every new email. Wish that wasn't the case.
I really like the S2 screen. There is something about it, the S3 cannot top. I do like the fact the screen is bigger on the S3.
One question I had was the charger. It came with a U.S. 110 Volt charger and not the European 220V. That was good to see. It is compatible with Samsung's other chargers.
I think this is the best price over the Internet: