So I've been playing around a bit with the Research builds in the Lab. I've been favoring the Zerg Defensive choices and the Protoss offensive picks so far. Although I did want to try out the Predator, I ended up going with the Hercules. I just saw more damage potential in that, although the Predators do seem pretty sweet (but I haven't had a chance to try them).
I'm really hoping that you can do a second play-through on Hard or something and unlock the choices that you didn't take. What have you guys been choosing on the SP Campaign mode?

I honestly never really used the predator, and I cant imagine that I would use the hercules either. Not positive off the top of my head but I think I chose all offense Protoss, and a mixed bag of Zerg, 2 offensive, 3 defensive. My favorites by far were the regenerating Mechs/Airships, Teach Reactor, and Automated Refinery. I feel that those definitely helped me out the most in the missions.