I upgraded from an Evo 4G that I got on launch day back in June 2010, and I have to say that the E4GT is a huge upgrade and well worth the price. The screen is far superior, the phone is significantly and noticeably faster and smoother (no lag whatsoever 99% of the time), a much better camera for photos and video (1080p on the E4GT, plus it's just far superior in quality to video recorded on the Evo) and the battery life lasts probably twice as long with similar usage. The build quality is much better as well (no light leakage from the bottom bezel or ill fitting battery cover). Also, I really like Touch Wiz much more than Sense, with a lot of useful features. And all of this in a significantly lighter and thinner body than the Evo. True, there are some areas that are worse than the Evo (especially the light sensor and some wifi connectivity issues), but overall it is a huge improvement over the Evo.
Personally, I wouldn't go the iPhone route unless you really like iOS (iTunes, etc.) and enjoy having a small display and one button. And I'm sorry but Siri is a joke -- like people are really going to start talking to their phones in the office, on the street, in restaurants and theaters, in airports, well, you get my point.