depends on your tank size as some can get huge, budget as some rare types can be expensive, and finally availability.
Dels if your tank is small (max 12"), ornati if you have a big tank for starters (max 20").
then for the rare spectrum, i recommend teugelsi, bichir bichir or congicus.
good luck.
I have to correct your info as Delhezi get to at least 14" and Ornates are the LARGEST Upper Jaw at 24"-28"