Let's see, way back in the day I played SC1 and Age of Empires 2 a lot. Then SC2 more recently, although I haven't touched it in a while.
Lately I've found more "tactical" and immersive games to be more interesting, like the Total War series. That'd definitely be my favorite. I've played Rome, Medieval 2, Empire, and Rome 2, all of which I liked for their own reasons. I just love the epic scale and the realism aspect, versus more "abstract" RTS's.