A wedding I went to recently had these little cakes instead of a wedding cake (and what a brilliant idea that was !) and they used the little cake size cases. They had them arranged on a multi-tier stand and they all got eaten - simply because they were just each a couple of bites of light sponge with a delicate icing, rather than a wedge of heavy fruit cake with thick marzipan and half inch of solid icing ! I can't imagine however, that it really matters which size is used though.... you will obviously get more (but smaller) cakes with the little ones.