They are exactly the same for arawana. 4×3=12 & 2×6=12. Both have 12sq' surface area. The question becomes what else goes in if anything? Breeding cichlids that need have caves far away from each other to reduce aggression then 6foot better. Big display drift wood as centerpiece then maybe the 4footer. I would measure different places in you home based on reduced traffic, indirect sun, interior wall with plugs, optimal viewing angles and direction of floor joist (making tank perpendicular). And let it best determines size or if your married ask you wife to decide that way it will always be part her decision and not just an other fish freak cluttering the house