hd2 is a gateway to a lot of OS
iphone 3gs is a gateway to a lot of apps
in hd2 you can experience any OS except few
in iphone 3gs you will experience quality apps and games
i know hd2 can run andriod and i am also andriod user but i have found Iphone apps and games more professional and handy
as far as battery timming is concerned hd2 can give you 1 day in exchange of moderate use of the phone
and in iphone 3gs it can give you almost 1.4 days in moderate use
camera wise hd2 camera is good but have purplish effect into pictures and noise too on other hand iphone 3gs got 3.2mp camera but can give you less noise
display wise offcourse hd2 have got an edge over iphone 3gs in size of the screen otherwise both are good
music wise iphone 3gs is far ahead of hd2
Choice is yours and money too 
Happy buying and do not forget to post pics if you buy any of these cellphones
as far as my preference is concerned i prefer apps games so i will prefer iphone 3gs but you have got the choice you flash andriod into hd2 and can have apps
Resale wise both are good to go
and yes iphone 3gs also got ios 5 update
again Happy buying:)
