Two primal, dark forces pitted against each other in an epic battle to the death! Who do you choose?
First, if we're talking a head-to-head matchup between one alien and one Sith fighter, I'd go Sith. The Force tricks, the speed, the intelligence, the fact that Sigourney Weaver beat one, all make me lean that way.
But the real power of the Aliens is when they swarm. So if we're talking about an Alien invasion of the Vader-era Empire, that gets a lot more interesting. Take the Death Star -- that thing has ducts and little hidden corridors all over the place. The Stormtroopers would, obviously, be meat. But then you've got a few Force-adepts running around, who can more than hold their own against some. But a whole ship full of gape-jawed, razor-taloned killers genetically designed to be the ultimate hunt object? I'd pay to see that!
Which would you choose in those scenarios?