Sponge cake, all the way. Bonus if it has multiple layers - sponge, cream or jam, sponge.
My least favourite type of cake has to be cupcakes, as the cake itself tends to be crumby and bland; I don't know how to explain it in words, but it's just not cake - more similar to bread. The icing is the best part of cupcakes; once that's gone, I'd rather just throw away the remainder.