I am currently thinking of switching to AT&T for the iPhone OR I can stay with T-Mobile and get the MyTouch 3G. What are the pros and cons of each and which would be better to go with? The reason I may not can switch to AT&T is the god awful prices. Help help help.

Specific Questions
-Is there an "App Store"
- Can it be used like an iPod?
-Do you get good service?


Thanks so much!