This one has caused me a great deal of brainache. I've never enjoyed Zenith- as I've said before, to me it just reads as a desperate attempt to do what Alan Moore did on (Miracle)Man and Captain Britain. If I'd never read both of those, if they weren't so seminal in my comics-reading as they were being published, Zenith may have been more impressive- but they were, and so when Zenith hit the prog I remember being disappointed that Tharg would print something so blatantly derivative. Plus, Steve Yeowell never did it for me as an artist. Nothing I've read by Grant Morrison outside the prog has impressed me at all, and much that I've read *about him* or *by* him in the form of biography has made him one of my least-respected writers in all of comics.
But he did Big Dave, which I love.
Ennis didn't do anything in the prog that I *love*- but his Troubled Souls/ For a Few Troubles More over in Crisis was as important to the teenage me of the time as any number of prog strips that I will happily laud to the skies. And, outside the prog, he wrote my second favourite run of Hellblazer.
Mark Millar is inarguably the most (popularly/ financially) successful of the three outside of 2000AD, but also not to my taste- though he has his moments.
So, all in all, I'd have to say that Garth Ennis was most successful in the prog, and Mark Millar outside it.
SBT