Both are very good restaurants (my personal favorites). Hard choice here. I agree with a previous poster that I like Jiko's bar better than Victoria's Falls. Great service there. They will let you try some African wines.
I think that the food overall is better at Jiko's, but both are very, very good. Probably better seafood at FF, but I'm not a big seafood fan, so this doesn't matter as much to me.
Boardwalk really is a fun place to hang out. If you are looking for a place to spend the evening, the Boardwalk is fun. There aren't a lot of places to get a drink if you are looking for that. The Yachtclub has a nice little bar.
In the end, I think I would chose Jiko's because I enjoy the food more, but you really can't lose with either choice.