MK II was the best, MK3 was undeniably the worst.
MK3 cut out most of its original cast, leaving you wit 8, plus one hidden character. After choosing your fighter you go to the "Choose Your Destiny" screen, where you choose the number of opponents you fight. Then you need to go the Kombat Kodes screen, where you can put in some combination of symbols that can influence the game. This is where the controll problems start. Trying to leave this screen is a problem, because none of the buttons respond to your presses.
Now you can start the fight. The first thing you'll notice is that the fighter's stances are not animated. They just stand there.
When it comes to the real fighting, you'll probably be sorely disapointed. The AI is incredibly cheap, because it always runs up to you and gives some sort of strong attack. If you do manage to get a hit in, it probably won't be a special attack. That's simply because the controlls suck so much. You have mabey a 1 in 15 chance of getting the move right, and the AI is almost guranteed to avoid it some how. Of course, the computer never has any trouble getting these moves to work.
Graphically, MK3 is a mess. You can't easily tell the characters apart, especially if they're pallette swaps. The backgrounds are also unrecognisable.
The sound was the final nail in the coffin. The sound effects are not only scratchy, but the music is hard to listen to.
There's really no reason to play this game. There are better fighting games on the Gameboy, and on every other system. Even if you're a die hard MK fan, you'll still hate this game.