Aliens are very strong, very fast, very stealthy. Presumably take on memories from initial host as 'Aliens' aliens formed a loose society based around the queen whereas Resurrection aliens were highly intelligent yet bickered much like their initial hosts (podded scientists if memory serves). A Predator could easily track an Alien and has the weapons to dispatch it with ease, however the sheer number of aliens in comparison to Predator numbers means any group assault would massacre any Predators. Terminators (T-801's) would find it difficult to track Aliens due to their speed and stealth however in a one on one battle a T-801 would rip any alien to pieces, probably destroying itself in the process. Also Skynet search patterns would easily corner alien infestations allowing nuking of the infested area. Terminators are also immune to being taken as hosts and as such any engagement would have zero possibility of increasing hostile numbers through capture.
Basically it all boils down to numbers. Terminators and Aliens are on level pegging in both strength and numbers as well as tracking ability. Predators are far less in number but their weaponry brings them level with both T-801's and Aliens. However if a T-1000 were to surface it would most likely, single handedly take down the Aliens and Predators.
