I played Red Alert but didn't like it alot, my favorite until now is Command & Conquer: Generals - Zero Hour. Before I knew that expansion I thought it was already great, but then I was like "Daaaayuum" because there were so many variations of gameplay style. I've played all the factions and generals and my favorite is GLA stealth and demolition generals.
Wait, did I say it was my favorite CnC games? Actually, it could have been Command and Conquer: Generals 2. It's a shame EA had to cancel it.
Yeah, that Demolition general was insane. Would also tank your framerate, but who cared?
CnC: Generals 2 might have been great, we'll never know. EA always manages to release the bad games but cancels the ones that look promising. Oh well. For now the series is dead, but one can hope that someday it'll be revived.