i vote starcraft becuase the complexity of the campaigns is exellent, i love being able to play as different alien races, the range of different types of battleground is a nice touch, and i just love the map editor
Right now i'm playing Diablo, but I don't think this is a strategy game.....
So I voted Starcraft - the best game ever (I really hate the zerg... )
Age of Empires and Heroes of Might and Magic are pretty good too.
Couldn't play W3, computer too old....
Command and Conquer: Generals rules supreme! It is far more dynamic in terms of gameplay then any other strategy games which i have seen. The cut scenes are also extraordinarily good. Just take the first mission of the China campaign. The cutscene when the GLA blew up the chinese parade was breathtaking.
I voted Warcraft, but SC is very close, just haven't played it for a while. I don't consider Diablo stratey, its just cut and slash. My true first love strategty game is Prelude to Waterloo by Talonsoft. Turn based tactical Napoleonic, it just don't get no better!
Combat Mission is also a lot of fun and an execellent simulation to boot!