What is better for an RPG gamer for a hand held system for xmas, a Sony PSP or a  

PSP is hands down the cadillac option. It offers so much to the owner beyond games. To an RPG gamer you might find the networking to be an extra bonus, being able to communicate with other PSP owners during a game a plus. The DS has this also, but the graphics on a DS are infantile in comparison.

I suggest you read the G4 article on PSP/DS comparison. It does a great job of breaking down the 2 systems.

Good Luck.

Which game titles are you looking for? If they are mostly playable in a certain hand-held, then that's your choice.

Its not really about which handheld is best but, the games that you are going to be playing. Then again, if your really into features, then you should again evaluate on the hand held that best suits your liking