Android is definitely a cheaper solution if you love apps and don't want to be on an expensive contract. I owned the iPhone 3G before and got sick of how slow it was. I now own a HTC Desire and its amazing however the keyboard is really annoying and I don't think you can match Apples keyboard - it has the best touch screen keyboard out there.
Lastly the iPhone has the better market because it has a lot more apps and it is more secure.