I voted Synodontis, and it wasn't even close for me... I've had, at some point: S. angelicus, S. decorus, S. petricola, S. multipunctatus, S. nigriventris, S. eupterus, S. nigrita (or one of the species of "lace" cats), S. serpentis, and S. ocellifer. I'm currently resisting the urge to add S. flavitaeniatus to the list...
S. angelicus is probably my favorite species. S. decorus is a truly beautiful species, and I think S. ocellifer is highly underrated when they have a gorgeous olive coloration.
I've never had much luck with Loricariids, and I haven't kept a lot of Corydoras (or related Brochis).