Mortal Kombat, most definitely. All the varieties and characters the game has had makes it a great game. I used to play it all the time. I really liked it.
Tekken all the way, there's already a Tekken 6 in Timezone, and so awesome! Way better than 5, 4, 3, 2, or 1! And I like Tekken 'cause it's cool and awesome. And the charaters and their story as well! But, I'm not starting a debate here!...