I have a 4G phone (HTC Evo) and while the 4G is fast, it's not really what it's cracked up to be. Browsing on a phone sucks, and even one with a big screen like the Evo. I find the 3G speeds to be sufficient for looking up stuff, but if you are one of those guys that lives on their phone (cough, Travis, haha) then the 4G might work for you. If you want to use the phone as a mobile WiFi hotspot then by all means, go 4G.
Be sure to check your carriers 4G coverage area, it's kinda hit and miss in outlying areas (suburbs).
I kinda resisted the smart phone for a while, but it's allowed me to keep track of the forum remotely and get a jump on priority emails. It's also a decent camera in a pinch and text messaging (that I swore I would never pick up) is really handy for a more private conversation, sending non time critical info, or keeping track of small data (addresses, phone numbers, dates, etc.) without having to resort to email.
Guess you missed the news.Get a carrier that has true unlimited data, stay away from these companies that are capping data because next they'll be capping your minutes. Go with either Sprint or Verizon, Verizon is more expensive though but better service.
I had the same issues with the HD2. Put every ROM I could find on XDA with terrible performance. Best I found was with vanilla 2.2. now have a MT4G running 2.3.3 and love it. Get rid of the HD2 if you can.HTC sensation. I have an HD2 running android 2.2 with sense, it's on the NAND. I don't like it. All the android conversions I've put on this phone have been glitchy, this one has been the most stable, but it still has it's problems. I have installed android on the RAM, the NAND, the SD card.... nothing is perfect. Ram is fastest though. Glitchier than my G1 ever was.
For the record, I've had 2 HD2's, both had problems.