Android is clearly the way forward. I replaced my rubbish Motorola DEXT with the Galaxy S and it is a brilliant phone! I have had mine since August, £30 a month for 16 months (first two months were free without any annoying cashback deals) on Vodafone UK.
There is lots of free software (unlike apple where anything good must be paid for). It is easy to root (jailbreak) and easy to install custom firmware. Do this if you want to install unauthorised software (I don't mean illegal, just not google certified) and it will run much faster and look better than Samsung's original firmware.
It has a scratch proof screen that works, in my current job it gets shoved in my pocket with a bunch of keys and the screen still looks brand new. The back is not scratch proof, but case-mate make a very slim but effective case for it. It is very easy to use and works well.
I don't use exchange so I cant comment on these problems, but all in all, a very good phone. Only thing it misses is a camera flash, 9.5/10!