SC was probably the most visually bland and uninspired game I've seen on any platform in the past 5-10 years. On top of that, the engine runs like shit.So yea, I've compared. Sins is the clear winner in that comparison.As for CoH... quite nice looking, but we're talking a small fraction of the units displayed.
I almost freaked out here when I thought you were talking about Starcraft...

Anyway, yes Supreme Commander is a nightmare to actually play with any real fidelity. My real concern with the game when it came out was that it probably won't actually even scale very well. There's this high peak barrier it's sitting on because of the... well, stupid engine design decisions among other things. Neverwinter Nights 2, anyone?
CoH looks fantastic and has a very distinctive art direction by contrast. It also has sane hardware requirements. I've never felt the need in any game to see 1000's of units on the screen like SupCom tries to do, but I can see that being a cool feature of a game. Valiant effort, but massive fail on the actual implementation as far as I'm concerned.
And by the way, Sins looks quite good overall, though I think some minor improvements could be made in several areas. It runs on ridiculously (by today's 'standards') low-end hardware, and that is a great accomplishment in any game.