Well what do you like better?
I love the AoE series of RTS games maybe my best. There are some nice newer games like, "Dawn of War Warhammer 40000 The Dark Crusade" (yes I know the name is long) that is rather mint as is the other game built on the same engine made by the same people and is almost identical apart from its WW2 not Sci-Fi, that si Company of Heroes, but I like DoW better, the Necrons hehehe....
But back to AoE presumably the best RTS out there what do you like best?
Age of Empires 1
Age of Empires 1 - The Rise of Rome
Age of Empires 2 - aka Age of Kings
Age of Empires 2 - The Conquerors Expansion
Age of Mithology
Age of Mithology - The Titans Expansion
Age of Empires 3
Age of Empires 3 - The Warchieftains
Age of Empires 3 - Asian Dynasties
Personally I have them all and love them all, while AoM is the cause for some EPIC battles with Titans and monsters of all sorts on EPIC proportions, it sometimes ruines the fun to have such overkill units...
Age of Empires 2 + expansion has always been a all time favorite, having spent an estimated 2000+ hours in the game includinf making maps some maps taking up as much as 100-200 hours in themselves with hundreds of triggers, My brother made the most awesome maps though, ranging from balanced RPGs that last up to 12 hours or simple survival maps and chase maps and the like. We used to play multiplayers with the family and guests with up to 8 players and were getting really good...
My brother Justin ended up being the best because he rushed to Castle age got 4-8 Town Centers right at the start pumped out up to 200 villagers then got Jannisarys one time he killed myself and 2 other good players single handedly using that tactic... I never had a chance hehehe.
While we don't play it that much anymore we still got lots of good maps and the skill is there, I will always remember it as one of my best PC games of all time!
Starcraft has a similar story with the maps and such but while my brothers took a fancy to it I might land at mot much more then 500 hours.