OK. Marzipan - fairly universally hated on a cake.
Royal (break your teeth) icing - fairly unpleasant when on a fruit cake, having been next to marzipan.
Fruit cake - beloved of old ladies and serious traditionalists, but fairly disliked by most right-thinking people. It's too heavy after a meal
Ditch the fruit/sponge option and opt for all chocolate - everyone likes that! We did. Everyone remembers it, everyone says 'Oh, that chocolate cake at your wedding..........Yum....'