On Apprentice, when I've got the time anyway. Lately that's been in short supply...
My decks generally fall into 3 catagories. Existing actual decks, serious type play decks that include cards I don't actually own, and fun (non-killer) decks copied off of places like this site, and elsewhere on the net.
I can't say I've run into the "Winners" you found, Fire Slinger, though I have played some people who were excellent players and had tournament grade decks to play. I'm sorry to hear you had a bad experience with it, but I think if you wanted to give it a try again you'd find plenty of people here that would be willing to play you, and I can almost guarantee they won't be packing Dojo decks.