I gotta go with Myers. Far to powerful, and hes sneaky and clever. I dont think it will be as big as his blow out against Ghostface, but it may be similar.
Alien has the reach, power, and speed advantage over Myers. Also, more weapons to work with. I see a finish Bishop style from Aliens.
I don't really know why but I went with Alien
Alien destroys Myers in seconds flat
If an alien tried to infect Michael I don't think it would take sense he's the embodiment of pure evil and they are just simply another form of life,regardless of how vicious.