My bets are on Michael. And this is why:

Jason: He's big and immortal, although he is in turn, a little on the dumb side.

Freddy: As long as you don't go to sleep, you'll be fine.

Leatherface: He's tough, but he's still a mortal.

Dracula: He can be killed at dawn or by a wooden stake.

Frankenstein: He's a human doctor! What's he going to do against these other guys?

Frankenstein's Monster: He isn't immortal...

The Mummy: He's waaaay too slow to be taken seriously.

American Werewolf: Last time I checked, werewolves can be killd by a silver object of sorts.

The Alien: This one can also be killed....Predator showed us that.

Pinhead: He's pretty tough, but he has died and as long as you can get him back in the box, you're fine.

Michael on the other hand, he has been shot, stabbed and pretty much damaged in every way possible, but he never goes away.

:)

Dont think Freddy has much of a chance here.
If he drags the Alien into one of his nightmares, it wont be of much difference because the Alien doesnt care about its sorroundings, as long as there's something living upon which it can pounce.
Freddy can create a daylight scene for Dracula, but because its a dream, Dracula wont be affected much either.
Some of these guys are pretty fearless, and Freddy will have a hard time getting into their heads and finding out what their worst fears are.

Some nice points covered ^ there. (though by Frankenstein, I did mean the monster, not the doctor)

Excellent points by DP & Doc. Although Pinhead can be killed and sent back to the netherworld too, and Drac also has his weaknesses. What about the Werewolf? Sure he can be killed by a silver bullet but do the other 9 know that? Jason or Michael dont go around carrying silver with them. The Alien doesnt stop to think about its killing. Its as fast as the Alien and can rip you to shreds in a second. But of course, it is dependent on the full moon...or is it?

hmm...

Dracula wouldn't have much real blood to drink in this fight. I would love to see a movie where Drac sneaks up on Jason and sinks his teeth into Jasons neck only to have Jason cock his head in confusion before swinging around and taking Drac's head off heh.

My choice obviously would be Jason. Some might argue that he has killed only humans before, but he did a great job of banging Freddy up nicely in Freddy vs Jason. As far as Michael goes, it will be interesting to see how he fares against Jason. Dracula might be a handful but decapitation does stop him in his tracks, and some of these killers are experts at lopping the head off. Frankenstein is a set of bandages and stitches, so can be taken to pieces in no time. Same goes for the Mummy too. Pinhead would be the only adversary who could give the others a tough time.

After pt.6, Jason didnt have much blood left in him. What about Michael though? Would he turn into a vampire if bitten by Dracula?

It would be interesting to think about the scene between the Alien and Dracula too. What do they do when against each other? Does Drac stand a chance against Alien's acid and teeth? or will the Alien turn if bitten?

The Mummy seems to be getting a bad "wrap" here. Depending on which version/mythology he DOES have a lot of supernatural powers. I think he'd be more than a handful, I wonder how an Alien would fight in a sandstorm because environment would play a HUGE part in this one. I think the werewolf against an Alien would be a hell of a fight to see too...

As far as the Aliens and Dracula, unless it was holy water those creatures were bleeding it wouldn't matter. Acid can't kill the count right? Drac would also have a distinct advantage when it came to picking his spot add that to his super strenght and intelligence and he'd have a fighting chance. Would he try to bite the undead or simply try and kill them? Dracula would probably be the smartest one in the fight and he could fly around waiting for his spot. Michael turning is a good thought but who knows if draining Michael of his blood would turn or kill him, it may just feed The Shape and make him stronger.

Hell yes. One of those lycans of Underworld would be quite a match for the Alien.

Of course the Mummy doesnt stand a chance without its powers. But given its all powerful, on its day, the Mummy can win against any of the 9 listed, or all of em. I think the Mummy is powerful enough to take on anyone.

Michael has been disposed off many times and has managed to return everytime. So I am thinking Drac's bite may not have the desired effect it should.

What if a face-hugger attaches itself to Drac and knocks him out senseless while planting an Alien inside him? Would we have an Alien with vampire powers bursting his chest and coming out?

or if the warewolf scratches an alien, the transormation would be death to all.