Honestly both could work. I have seen many groups of geos do well together, I have also seen many that have not been successful. It depends on the personality of the fish. Solo could also work successfully depending on tankmates and tanksize, I would recommend you keep them with other peaceful cichilds that they can interact with(severums,electric blue acara, etc). I am quite new to geophagus to so this is just information I have read online.