external is better ass you don`t have this big black box in the tank plus it acctualy adds (only a few litres but it all counts) to your total volume, aswell as being alot more flexable with your media as instread of maybe 2 or 3 compartments you have 6 or 8,
i personly run a fluval 405 and a rena xp2 on my 220 lire tank,
i only run an internal on my 4 gal hex tank as there isnt a external small enought for the tank