That completely depends on what you consider to be the attributes of a game that makes it the one of best.
http://www.gamespot.com/gamespot/fea...games/p-5.html
http://gameinformer.com/b/features/a...issue-100.aspx
Its sold 9.5 million copies world wide. It only sold 1.5million its first year so the rest has been over the past decade.
Its considered a professional sport in Korea with 2 dedicated cable channels and where matches can draw 100,000 ppl in stadiums/arenas, and e-gamers can actually earn a living there through tournaments. 4.5million copies have been sold there.
It could only reach that status if the game was perfectly balanced. If there was a dominant race or dominant strategy in the game then everybody would use it and it would not be as popular. So that is a testimony to its legendary balance. People still play it. And what more do you look for in a strategy game than depth and balance?
There's a lot more but I'm feeling lazy..
So to you .. whats the best RTS ever made so far?