Hmm....Well, if you were to get only one, I would suggest the MKA: Premium Edition.

You get MKA, which has all of the characters, and then you get UMK3 a good classic MK game.

Shoulin Monks is an alright game.

If you're simply trying to collect the games, get them all, but if you want the good ones, get nastolgic.

get shaolin monks its got the best storyline

MK: Special Forces


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Kidding.

I'd say one of the 2D games or Deadly Alliance would be the way to go.

Actually, Shaolin Monks has a pretty butchered and non-canon story, and the dialogue/voice acting from Liu Kang, Kung Lao, and Kitana is outright painful.

But it has utterly awesome gameplay. In fact, I would say it is the greatest Double Dragon-style two player beat-em-up ever made in the history of video games.

As for the fighting games, Armageddon is your best bet if you like your rosters huge...but Armageddon is essentially a rushed, unfinished mess with very little story and bonus content. Deception is the best COMPLETE MK game.
Deadly Alliance was great, but Deception is DA's engine improved, so there's no point in getting DA because it'd be like a step backwards.
Unless you're all about the story, in which case, you need all three games, DA, Deception, AND Armageddon.

I recommend Deadly Alliance and Deception.

Those were the last true MK games that we got. Shaolin Monks was fun but the story and gameplay are not truly "MK."

MKA gives you all the characters but in quantity over quality. So MKDA and MKD are the best choice, imo.

MKDA for the story and for being an excellent re-introduction to the series. And MKD for its dark-fantasy, flashy MK-style ambience and design.