If I could keep only one kind it would be Polypterus palmas polli. Stays relatively small (about 12-14 inches), has a nice pattern, and is usually very active and full of personality.
Based only on pattern, I'd say Polypterus delhezi.
Based on rarity in the hobby it would be either Polypterus ansorgii or Polypterus teugelsi.
-Joe