Fondant looks great, but I wouldn't want it on my wedding cake. Most people just scrape it off and there's all that hard work for nothing. It doesn't taste that good, and has kind of a rubbery texture. The main advantage of fondant is it keeps the cake moist and allows decorators to do things they can't do with a buttercream. But I'd still rather have a buttercream.
Also, a buttercream should be made with real butter, not shortening. Shortening will make it greasy and waxy tasting. A vanilla buttercream will complement most fillings and cake flavors. Sometimes, sticking with tradition isn’t such a bad thing.