We have a Gamecube and Xbox. The Xbox is highly favored, where the Gamecube is just ok.
I have a 7 year old, and a 9 year old.
They are the same ages as your kids.
The Xbox has more mature type games. We don't allow them in the house, but my son like the sports games (Football, tony hawk, Amped, etc). We have other fun games like Crash Bandicoot, Star Wars, Fuzion Frenzy, Shrek, Spongebob, Spiderman and a few others.