I do far more no-gi because I find it funner, the numerous grips in gi grappling annoy me, and I want to be able to effectively operate without over-reliance on extra techniques from clothes. I've seen guys who are great with a gi and terrible without one. That sucks if you get into a fight with grappling involved and you try to rely on grips that aren't there. That said I need to do a little gi work, if you can escape with a gi then it will be easier to escape without one. That's the main benefit really plus it just builds awareness with the extra options (as irritating as they are to have done to you). I doubt I'll ever really use much in the way of offensive gi techniques though, my no-gi skills are way too ingrained.
Member of DaJoGen MMA school under Dave Hagen and Team Chaos fight team under Denver Mangiyatan and Chris Toquero, ran out of Zanshin Martial Arts in Salem Oregon: http://www.zanshinarts.org/Home.aspx