Go old school with Street Fighter 2. The original Mortal Kombat is great, but not nearly as balanced as Street Fighter 2.
I remember going to friend's birthday parties in elementary and junior high school where we would have a Mortal Kombat competition. Many of my friends played the game more than me and could easily beat me 2 out 3 times. Well, I won quite a few matches by cheap-shotting them with jump kicks to knock them down, uppercuts as soon as they stood, another jump kick, another uppercut, and mister "I spent 6 hours last night practicing" didn't even make it out of the 1st round.
So yeah, old school is the way to go. If you go 3D, I would recommend Virtua Fighter.