filters question

Well, they are 2 different types of filtration methods. I find both easier mainteance and more effective than hang on the back type filters . However, they are also more costly up front.

It really depends a lot on your tank, size, what you are keeping, etc - and what you want to accomplish.

All filters are effective for the right situation

I've gone through two canisters on my 75g in the past seven years, and I have to say that they're definitely worth the money. However, they can be a pain to change/clean the filter media in, whereas the Emperors (I've had no problems with these either) are much easier to clean/change. I haven't been able to really notice a difference between performance between the two.

About the only time you'll notice a big difference between a HOB and a canister is when you have a very large bioload, either from a heavily stocked tank, or from a tank stocked with messy fish. I found that no HOB filters can do the job that a canister does when it comes to a high-bioload situation, because a canister moves a lot of water through a lot of filter media, resulting in more efficient biofiltration.

If you are planning on a light to moderate stock, a HOB such as an Emperor is fine. Heavier stocking requires either more than one of this type, or a bigger gun like a canister. They're worth the money in the long run if you stock like I do...