I currently have both running. There are some very good HOB filters, but I have to say my personal favourite is the canister. You can put the spray bar/outflow where and how you want it, and they are quiet. The only drawback is that you actually see more pipes with the canister filter - on an HOB all you see is the intake, but a canister you can see the intake and the spray bar unless you try hard to hide them. Canisters are also more efficient filters, IMHO. I have two Eheims, but I've heard good things about Fluval as well...