It depends on what you mean, but I would venture to say that few would argue with Johns Hopkins. Some may say Mass General also. Granted, these are academic places (i.e. research) that receive an enormous amount of money for research. So rather or not you're a better clinical surgeon when you're done, I can't answer that. You will have a lot of connections though.
I apologize to mpp, but I hear that the attendings at Mayo are a little too hands on for general surgery. Also, you may not do enough bread and butter surgery at Mayo. But I don't really know so you tell me. Anyway, Mayo would probably be a good place to do a fellowship.