Here's my opinion. It's true that the hood filters function the same as a HOB
filter. I have a 5 gal
. tank with a hood filter and to be honest I really can't stand it. It's hard enough to get into the tank to do any maitenence as it is due to its small size plus there's a filter in the way as well. I'm not sure if all hood filters are like this but the lid for the hood opens over the filter. So when the lid is opened, there's crack no bigger than an inch wide between the filter and the edge of the hood. So anything other than feeding the hood has to come completely off making it difficult to see what you're trying to do in the tank unless of course you have a good amount of lighting that the tank is in. The only real advantage I see in hood filtration is that you don't have equipment hanging on the back of the tank, but even still, that's what a background is partially for right?
There's a lot of debate on undergravel filters. The main opinions that I've come across is that they're a thing of the past.
Canisters are great for larger tanks. I've personally never used one. I was going to get one for the tank I just got but then wound up getting a 180 gal
. which is bigger than I had originally planned so I have a wet/dry filter. I've never seen canisters come close to that size but not quite. Anyways, canisters are nice because to do have the option on which filter media you can use and the maitenence period is supposed to be a bit longer than a HOB
filter. I've heard horror stories about fluvals leaking though.