i am a fan for both android and WM.i have BB and htc hd2 and my friend has the desire so i know it well.
browsing on the desire is better than the iphone because of the screen size which makes a huge difference imo even if the res. of iphone 4 is better.
and opera browser is top notch and very fast,sometimes faster than safari and the other way around.you can also download skyfire browser for some flash contents if you like and i use it occassionally.
about the screen resoltuion,retina is sure better but the htc screen is not crap by any means.
the clear advantage of android and WM is obviously customizability.i flash roms all the time and there are many free programs and roms on xda developers if you are into that kind of stuff.
finally battery life on any android or wm phone is crap.no way around it.you will have to charge it every day if you make some calls,check emails,few browsing and a couple of youtube video.i really wish that mobile companies make some serious developments for batteries.