the problem with martial arts that it's an art
teaching kata's and air punching the whole training won't help you 'in da streets'. But I do reccomend traditional ('eastern') martial arts like full contact taekwondo, Kyokushinkai karate and jiujitsu (if there is enough sparring involved)
Eventually a good MMA fighter is some one who knows how to perfectly combine a lot of martial arts and fighting sports. Most MMA fighters are good at thaiboxing (essential stand-up), Brasilian Jiu Jitsu and wrestling.