I was in a similar situation. I went with a Pentax 645. MF works much better for me.
After having used the 645 for three years, I still want a larger negative.
I don't really use my 35mm kit for anything more than a loaner for close friends or a rainy day walkaround camera. It's tough to say what would be best for you but i'm glad I bought my mf camera.

ps- the zoom lenses for the p645 are supposed to be pretty nice. I know that's not what you were looking at, though..