At the moment... WoD, but only because I have a whopping one character I can be dredged out of the mothballs once in the bluest of moons to play simply because I
her... and she's been played all of twice, total.
Over all, and hence the vote: original theme. I've spent more time and put in more RP hours on games like Nightscape, Shangrila, Ghostwheel, Castle D'Image, Cybersphere, and similar places by a huge margin than I have on WoD games. While old games are old, I put in a lot more hours on them than I can be bothered to invest in a WoD game.
In terms of practical hours in the hobby, most of my time these days is spent staffing/developing stuff for games when I'm not rambling about stuff here, and there, too, 95% or more of that time is dedicated to an original theme/system game, with the remaining 5% giving wiki advice or helping pitch in with that for folks if they ask.