I've never used a Windows phone nor do I know of anyone who owns one...
As far as WP goes, WP6 and before was horrid. I haven't used WP7 yet, but it's gotten very good reviews. I'd check it out before making a decision.
Also I'd go with the iPhone myself. In my opinion it has the better OS and I just dislike smartphones that aren't iPhones or Windows Phones, but since Windows Phones aren't part of the discussion I say iPhone.
[Edited by yosup, 12/1/2010 6:39:09 PM]