Iv got the HTC HD2 and its an awesome bit of kit, I dont know why people are saying its buggy or unreliable, I use it all day with multiple programs running all at the same time and its still fast flicking between the different programs and apps, Iv never had an iphone but i do believe this is something the iphone cant do (or maybe I will be shot down ha)
Internet on this device is very very good it is flash compatible and I am yet to come across a site that wont work, although I have been using it on wifi as apposed to through the phone as it is not very quick that way.
Battery life sucks balls though so I am going to purchase another battery yes it really is that bad especially as I have downloaded coreplayer so I can watch my AVI downloads without conversion on the large 4.3" screen.
I would not swap this for an iphone for love nor money, but this is my biased opinion only
Good luck in your decision Im sure whichever you choose you will be more than happy with as they are the leading phones at this present time for their own reasons.