All your base! NAO!
Starcraft, Dune 2 and Total Annihilation.
TA has it all! Huge maps, great faction balance, insane maximum unit cap, resources in abundance (if you know how to work the map and your tech tree), good AI, reliable internet support for those 4 vs 4 fights and lovely graphics. Graphics that were revolutionary for its time, and i still find the game aesthetically pleasing.
For me, this is how a RTS game should be. You are truly the architect of your own demise or your foes demise. There is nothing random about this game, Its all about tactical gameplay and micro management, thus the best player wins -- everytime.
The audio department is kind of "meh", and the level design can get a bit monotone after a couple of months, but thankfully you can download a myriad of new maps from 3rd party developers, that being TAs near-fanatical fanbase. Oh, and there are probably 500-1000 unique units developed by above mentioned individuals that are free for download as well.
I will recommend this benchmark game to anyone, even in these modern times.