Maxon rules. I have 4 Maxon overdrive pedals and have used them for years. Neither the Ibanez or Fulltone can beat the VOP9. In fact, the VOP9 is just an OD820 in a smaller casing. I have both a VOP9 and an OD820. They sound the same. I've been back and forth with the Fulldrive II mosfet over the years, and while it's an impressive pedal, I would NEVER prefer it over the VOP9.
I've heard people say it's a Klon Centaur killer. I know Klons are extremely good pedals but I'm so satisfied with my Maxons that I never bother seeking out another OD. Very awesome pedals. Check out the Maxon AD999 analog delay too, it's one of the best.