I have some experience with both dr's.
I went to Joseph Leveno when my dr was out of town with my last pregnancy. I really liked him. The only thing I didn't like was that he didn't do his own sono's, but that is a personal thing since I'm used to my dr doing his own. He has never been my regular dr, but I liked him and saved his card in case anything ever happened to my dr.
Dr. Fong was my dr's partner when I was pregnant with my first. I would highly recommend him. He is very kind, thorough and seems to be up on the latest. I also liked that his wife was also his nurse (don't know if this is still the case). She was great and they really seemed to work well as a team. They have children of their own and seem to understand what pregnant women are going through. I had a lot of problems with that pregnancy, so I saw him several times and he (and she) was always reassuring.