Xperia has a touch screen and a game pad. It also has a larger screen and games like crash bandicoot. Theyre very expensive though. I want one.
iPhone has a gigantic library of apps for probably everything you can think of. the screen is smaller though. Thats all I can really think of.
I, personally, would go for the xperia, just cause it looks flashy.
Summary:
Xperia: Gaming phone
iPhone: Inspector gadget in your pocket with small games