Do you already use itunes or google services, and are you going to want to integrate your phone into other areas of your life? or do you just want a nifty phone and that doesnt matter so much?
For me, I use google for anything I can, so getting a droid was a no-brainer. Contacts, calendar, gmail, task list, gtalk and such, and i knew i could get apps to do most of what i wanted with my pc/network on it.
My friends have lots of apple devices (apple tv, ipod touch, ipads, macbook), and only got a droid because they wanted a smartphone and our carrier doesnt have iphones. theyd kill for an iphone.