I agree with @fishguy1978
: you can keep shell dwellers and Julidochromis
together, but that's unlikely to work in a small tank. This is a 48" x 12" x17" tank that contains three breeding groups (left, center, and right) of J. ornatus
plus several pairs of N. multifasciatus
. The adult ornatus
don't bother much with the Multi fry- they're too busy breeding and defending their territories- but once the J. ornatus
young put on some size, then they will prey on the Multi fry. That's not necessarily a bad thing unless you have a way to sell the inevitable abundance of Multi fry.
In terms of which are fishes are more interesting, I agree with @knut_
that this is largely a matter of personal taste. Multi's are cute with their small size, constant digging, and ritualized aggression, but my favourite shell dweller is N. brevis
form very stable pair bonds, with the much larger male defending a single shell (usually) that contains his tiny mate. N. brevis is also very pretty-
The one shell dweller I would avoid at this point is Lamprologus ocellatus
, because you're just asking for trouble with such aggressive fishes in a 20-gallon tank.
That said, there is nothing quite like a breeding group of Julidochromis
, with fry of various sizes cohabiting a territory with their parents. And Julidochromis
are largely unconcerned with gravity, so you will find them swimming at odd angles, even upside down, amongst the rockwork. For me, a tank of Julidochromis
, especially my favourite, J. ornatus
(below) is hard to beat for interest value.