I've really enjoyed the sch-u740. Whether I want to admit it or not, I'm an active text messager and the qwerty keyboard really makes this process so much easier. I decided not to spring for the $15/mo. for internet just yet, so I can't speak to email capabilities, browsing, etc. My brother has a Sony Ericson phone and I'll admit I'm a bit jealous of his ability to add many applications and customize his experience.
I have also used it for picture messaging a fair amount and find the process incredibly easy and the pictures turn out just fine considering the cost and size of the phone. One complaint I have is that in order to use the alternative characters for each button (e.g. type a number or punctuation while in ABC mode) you have to hold the key down for a full two seconds. Sounds minor, but when pounding out a phone number in the middle of a text message, it gets frustrating.