Being someone who actually does make wedding cakes, I would say it would depend on what you want to achieve with your cake. Some looks are much more difficult to create with buttercream than fondant, and if they are possible they are usually much more labor intensive which will add to your cost. Not all fondant's taste bad, but that depends on the baker. There is also something called a buttercream fondant which is very good actually and tastes very similar to the buttercream frosting, the only drawback is how shiny it is. I say, talk to your baker about what you want, and what he (or she) could do with just the buttercream, taste the fondant they would have and go from there!