Supreme Commander: Forged Alliance with the LOUD mod is the greatest RTS ever created. Nothing modern gets even close to the level of detail and scale this game has. 10s of thousands of units all with real projectiles can than be dodged.
Get some friends together or play by yourself. Up to 16 players in a match.
Awesome AI with lots of configuration so Co-Op play is actually fun, you can tune the AI easily to present a challenge but still not get wrecked instantly.
It's not really a rival they actually work more collaboratively. FAF is aimed at competitive PVP while LOUD is aimed at co-op / Single player.
To that end, other communities have seen fit to begin adopting some of the principals involved in that performance, and I'm all for it - being that it's a good thing for the entire Supreme Commander experience. I'm going to specifically mention Jip (from the FAF community) who has made every effort in that regard, and we consider him a valued friend of LOUD, not only as a regular user of it, but in his efforts to break down the walls between different communities and bring them together.
^ Quote from their mod page, their devs share notes on Performance Improvements that both mods included.