Mind if I ask why? I have some friends asking me about the differences and I only really know iPhone 4. Figure if you're switching it has to be for a good reason.
honestly its just a matter of preference and ease for me. i use macs at home and work on macs so i like the compatibility factor of iOS. plus i used to have an iphone 3gs so ive got a nice library of itunes and apps that im anxious to use again. the droid x is a great phone and has never given me a problem, i just miss my iphone