I don't have a data plan, and even though windows mobile does so much more without data, I still feel that Android is the better choice for me. I can still get apps (though most of them are warez which I shouldn't speak of :P) and do all the basic things you usually do with phones. What I really like about Android over Windows Mobile is that you don't have to always close the apps you use, the UI is much cleaner, and the keyboards that you can use.
The thing I like most about Android is the keyboards. I especially like the HTC IME because it's pretty much the same as the keyboard on my iPod touch, but has tactile feedback (it vibrates when you touch it). The Swype keyboard is pretty nice to have too.
This is just my preference, because I am a heavy texter and the keyboards that android has fit my needs better than the crammed keyboards that windows mobile has.