Frosting is much tastier in my personal opinion. Perhaps it's psychological on my part because fondant looks so much like play-food, but it tastes and feels weird when I eat a cake covered in it.
Also... this is *completely* snobbish and I fully admit that, but! My mom and a few other people I admire used to make elaborate birthday cakes for us/their kids when we were young, all of them using regular frosting. Fondant is basically made for shaping, so it seems a little like taking the "easy"* way to me and I'm more impressed by the traditional cake decorating methods.
*Though please let me add that I do not in any way believe that people who are creating such amazing cake sculptures out of fondant are having an "easy" time of anything! It's still a learned skill and creative talent.