Original for me. There are a lot of great fan comics out there set in pre-established universes, but especially as far as anime and manga goes, there just aren't enough series I care about enough to get into fan work of. I love looking at fan's takes on character designs and whatnot in DeviantArt; but looking at those pics is a no-commitment deal. I'm not reading a multi-dozen page comic, I'm just clicking a link, looking at x redrawn with y style, and clicking "like."
Part of the appeal for original comics is, for me, the mystery. I don't know these characters. I don't know everything about them. I'm reading to learn about them in their first established adventures. And, knowing that their original art, there's the excitement of possibly one day, years and years down the line, seeing them pop up somewhere and being all "Oh, I read that when it was online only." /hipster kitty