I'd say good pitching, good hitting, and good fielding are most important...
I'm not sure one is more important than the other. I've won with teams that scored 1000 runs. I've won with the best pitching. A lot of it depends on the dynamics of your league. Really, I think you need to be great at one of them and generally above average at the other. But I don't think one is more important than the other.
my two cents...