Two choices I recommend- 1. iPhone 4S, because well- its an iPhone! And it has Siri, iOS 5, and iCloud- It just works well. Especially on AT&T's 14.4 Mbps HSDPA network for iPhone 4S. The dual core (Underclocked to 800MhZ) processor also gives a boost. Also the iPhone 4S's 8MP Camera with all new optics is amazing.
If you want the latest and greatest- then get the Samsung Galaxy SII Skyrocket. It has a 4.5" display, 1.5 GhZ Dual Core Qualcomm Snapdragon Processor, 8 MP Camera, etc.
If you want a phone that will last, then go with the iPhone 4S (It won't be replaced by another iPhone in a year or so). (But a better Android phone could come along...)
The Samsung Galaxy SII Skyrocket already is obsolete! The Galaxy Nexus is almost out in the U.S (Verizon) and is running Android 4.0 Ice Cream Sandwich, 4.6" display, etc. Also so many other phones like the Droid RAZR and the HTC Rezound. This phone will become nothing after a "2 year contract". Hope this helps.
If you want an android, get the HTC Inspire, HTC Vivid, Samsung Galaxy S 2 Skyrocket, Samsung Galaxy S 2 regular, Samsung Infuse or the LG Thrill. Otherwise go with a blackberry for something a little cheaper.