Hmm....
Depends on the bottom dweller. IME there are quite a few who look fairly different, so for the ones i keep, based on the now patented -germ- Cool Index (or GCI);
Hillstream Loaches = Yoda cool; Interesting looking, cute with an edge and all around a little different.
Parotocinclus = Mr T cool; Tough looking, serious and seriously cool.
Otocinclus = The Fonz cool; Pretty average looking but not without their old fashioned charm.
Panaque Maccus = Beatrix Kato cool; Gorgeous looking with interesting behaviour, but i don't see enough of them.
Are you looking at buying a Bottom Dweller yourself or just getting opinions?
If you are planning on getting one just ask and i'm sure you'll get loads of reccomendations....