This is a really interesting article, I love reading about game networking. Hard to find many resources on this type of stuff... the 'Age of Empires' Gamasutra one is awesome too.
We used Apple's Game Center API for the online portion of Stratosphere: Multiplayer Defense (iPad), and it was pretty nice that Apple did all the work as far as network packets go... but you do have a choice between reliable and non-reliable sending. It wasn't explicitly said, but we assumed one was TCP and the other UDP. We went with the reliable option for all of our packets and it didn't really prove to be a problem, even simulating under 3G. Granted, Stratosphere is a strategy game. The bigger problem ended up being just having enough people online at one time to even play lol.
We used Apple's Game Center API for the online portion of Stratosphere: Multiplayer Defense (iPad), and it was pretty nice that Apple did all the work as far as network packets go... but you do have a choice between reliable and non-reliable sending. It wasn't explicitly said, but we assumed one was TCP and the other UDP. We went with the reliable option for all of our packets and it didn't really prove to be a problem, even simulating under 3G. Granted, Stratosphere is a strategy game. The bigger problem ended up being just having enough people online at one time to even play lol.