Do you prefer games with (mostly) symmetric factions like in Homeworld and Total Anhilation, or asymmetric like StarCraft ?

From a competitive point of view, symmetric is more "pure" (chess is symmetric, for example) , but asymmetric is more fun and unique, in my opinion.

To answer the title question, yes.
If factions are properly implemented, it doesn't matter if they are symmetric or not. If factions are badly implemented, it still doesn't matter if they are symmetric or not.

Then again, the same is true for any game feature. Well implemented ones are good, badly implemented ones are not.

P.S I've enjoyed C&C Generals, Starcraft, Dawn of War and Master of Magic which have assymetric factions as well as Civilization that has symmetric ones. Can't recall many others with symmetric factions though. Not sure where Master of Orion should be, symmetric or assymetric though.

Can't really say I have a preference and I've played everything. I enjoyed Meridian: New World and that's completely symmetric, and I've played StarCraft and that's completely asymmetric Then there's Outpost 2, which is mostly symmetric, Warcraft 1 and 2 that are mostly symmetric, and the Command & Conquer series which is mostly asymmetric. I've enjoyed them all.

Age of Empires series and Rise of Nations are probably my favorites and they're more symmetric than not.

I prefer asymmetric factions. If the factions are symmetrical, what's the incentive to choose one over the other, except for their window dressing or back stories?

Personally I prefer asymmetric factions, that way you can choose one that fits your playstyle. Also, factions that are different in more than just name and graphics give a game more replayability imo.

For single player games, definitely assymetric. Definitely assymetric. Some races are much more powerful than other, while other races always struggle. I always feels sorry for the bears, birds and cats...

Asymmetric for me too I think. It's more fun and varied that way as each side usually has its own play style and plusses and minuses.
Plus is don't play multiplayer which is where the balancing flaws in an asymmetric system become more apparent.

Asymmetric.
The same reasons as the other posts with variety.
I'd add difficulty too. It's nice if some factions are better or worse than the majority so you have another way of choosing your difficulty level. It's the same with maps. Balanced are good but sometimes I like to start in a good or bad position.