Tekken 6, Tekken has better music, air combos, more characters, and has that Tekken feel to it.

SCIV just has lots of unlockables like artwork and weapon demonstrations.

I'll still be getting both but Tekken just has that aggressive hard hitting feel to it that gives it the edge over SC IMO.

There are several good games for the Xbox that stand out from the rest.

Most notably:

Halo series, Ninja Gaiden, Dreamfall, UC2: The Liandri Conflict, DOAU2, FatalFrame 2, Fable, KOTOR/Jade Empire, gunvalkyrie, and every game that is on all 3 consoles always runs best on Xbox (i.e. most consistent frame rates).

I'd say Halo is better then Fable. Both are easy to pick up and play but Halo controls and runs smoother and is overall more fun to play in the long run (especially if you have Xbox Live).

Of course there are several other good games on the Xbox as well like Ninja Gaiden, Unreal Championship 2, Dreamfall, Jade Empire, just to name a few others.