The reason I mentioned that you might want to go with an Emperor is the ease of maintenance and the Bio Wheels. The Emperor is very easy to maintain...yank out the dirty cartridges and stick the new ones in. It's easy to tear down and clean when it needs it. It is very reliable (no more than the canisters though). It has the bio wheels (which you can add to a canister). The advantage to the bio wheels is you can change cartridges or even tear the filter down and clean it without disturbing the biofilter. Marineland makes a Pro 30 and Pro 60 bio wheel setup that can be plumbed into the return line from any canister if you decide to go with that. You might have noticed that I like bio wheels on FW
Now, if you don't mind a little extra work when cleaning the filter, by all means, go with a canister. The canister will run longer between cleanings so you don't have to service it as often as a hang on back filter. It will suck every particle of trash out of the water leaving it, as previous posts have said, crystal clear. Another advantage to a canister is that you can put the tank closer to the wall as the only thing back there will be the hoses going to the filter. Each system will provide excellent filtration...it really depends on what you want and how you want to set the tank up. As I said before, if you plan to inject c02 into this tank, go with a canister and don't use the bio wheels. With c02 injection, you want to minimize surface agitation as much as possible to keep the c02 levels up. Yet another advantage to the canister is a greater choice of media...say if you want to use peat moss.