this is a great b'cream recipe
an all butter american buttercream (powder sugar and butter) or a SMBC or IMBC with butter recipe is going to chill the firmest to create a smooth under layer for your fondant. I know some people have luck with a shortening based buttercream under fondant, but I just prefer a firmer surface to work with on smoothing and maintaining sharper corners. THat all said, I usually always do a layer of ganache on my cakes to smooth before applying fondant. That makes the longest lasting surface for me and holds up best in my climate's heat.