Depends on your current filter(s) and the fish load you have, or plan to have.
Some cichlids can be nasty while eating, and all need the best water we can give them. Personaly, I'm rather paranoid about things and tend to over do it. On my 4ft. 75 gallon, I have a Rena XP3 and a Emperor 400. I have the HOB on the left side, the intake for the canister close to the middle, and the return from the canister on the far right side. Also on the 75 under the rockwork I have whats referd to a Under Gravel Jet system. This is just a series of pvc pipe with a pump hooked up on one end to create water current from the bottom, and really does a great job of keeping the sand clean by keeping uneaten food and other debris in the water untill one of the filters can pick it up. On my 3ft 45 gallon, I have a fluval 404 and a tiny HOB to break the water surface to keep the surface film from collecting.
Canister filters have biological filtration as well. Very effecently too.
I don't know if you can run the HOT filters under the tank or not as I've never had one to play with. But you got a good deal on them sounds like, so if I were you I may keep them anyway just for a backup. I would go with a medium sized canister filter, and a medium HOB. Or if you only want to do one filter, you may want to try a medium-large canister.