I'll have to say Predator 3 as well, I always was more of a predator fan since they are more of a civilized species (well, depending on how you define that), with a culture and things like language and customs to discover. Not that I have any hope that Fox won't completely screw that one up, but ideally speaking it's still the species I'd like to see more of.
The aliens, while I like them a lot, feel mostly just like bugs with a fairly primitive and predictable behaviour to me. Nothing wrong with that, it's partway what makes them so terrifying, but it also makes me feel there's nothing more there to discover really, they can give them more screen time, but unless they go and change what they essentially are like in Resurrection, throw in a new reproductive system for an extra twist or something, it kinda feels to me like there's nothing new under the sun there.
The only case where I'd prefer an A5 over a P3 is if they threw in the Pilot race, their connection to the aliens, and did it the right way.