there are so many different aquatic creatures that hold my interest, i dont think i could ever have just one system.
african cichlids (mbuna & utaka), discus, dwarf cichlids, morimids, polypterus, fw eels, labrinth fish, schooling tetras, low light planted, high light planted, outdoor ponds, exotic koi, tank buster south americans, large predators, rare plecostomas, exotic catfish, aquatic reptiles, the list could go on all day and my salt water list could be just as long
soft coral, LPS, SPS, clams, anenomies, gorgonians, inverts, grazers, plankton feeders, predators, tidal animals, cephalopods, cold water, etc...
perhaps in the future well even have deep ocean presurized and thermal vent biomes.
i just could never pick a favorite.