I'd love to see 1 alien, vs 1 predator vs a cannon fodder of scared shitless marines.
One thing to keep in mind about "first encounter" scenario, it's not like it would make a difference to the alien. They have no allies, they attack first and don't bother to ask questions. That wouldn't bode well for an inquisitive predator. But then again if the predator just watched the alien slaughter marines and examined human defenses and counter attacks, that would be cool.
Damn, now I want to play the old game.