IMO get the external canisters. My hang on filters are solely there whilst I save up for enough for 3 externals. The hang on filters are great, mine were 10 quid each from all pond solutions and work perfectly. But I would rather an external for aesthetic purposes as well as the fact they distribute water flow more efficiently. I notice with hang ons its hard to get flow completely round the tank. But they are great if you don't have such big hard scape blocking the flow like my middle tank.