I think most people would say an Eheim external. They seem to have the best reputation on this forum. I have 2 Fluval 304s (older model) on my 75 gallon tank and have been very happy with them. They'e been running for almost 3 years now. Regardless of the brand, I strongly suggest an external over HOBs and for a tank of 4' or more, I would also suggest dual filters and heaters, one on each end, for better water circulation and temperature control.