Fondant or Buttercream

Well I guess you know my vote.

Fondant looks great but...
~ it is hard for the bride and groom to cut through
~ it makes more work for the catering staff when they cut the cake to serve it (they may or may not peel the fondant off before serving)
~ it doesn't taste like anything

Buttercream can be made to look as smooth as fondant (look for a skilled artist).
Buttercream tastes better and comes in a variety of flavors.
Best of all, it costs less than fondant.