I would just go with the one with the best deals. But Steam's service is hands down the best for buying PC games. Once you buy it, you have it forever on that account.
But I would recommend Steam. No questions asked.
New turtlebeach headset
Dazzle capture card
Rock Band 3
Fable 3
FPSFreek xbox 360 analog stick extensions
uhhhhhh and moneh. Also, what ever my parents give me.