"Mostly" would have suited me best, as well. If the current trend holds I'll just be DMing 3/4 of all the games I play, though. (It used to be more like 90-95%.)
I voted sometimes, but it's really closer to always. I'm the always DM for a weekly group, an often DM for a near-weekly group, and a player only in two once-a-month groups.
I DM a game and I play in one. It's a nice balance for me as I don't think I could do just one of them without burning out. It also helps that my current party members aren't a bunch of re-res either.