ok imm a give a more detailed run down of my experiences to help everyone. OK ive owned both Emp 400 and many ACs (mini, 2 150's, and a 300). My experience with the emporers was good, but i would not say as good as an acquaclear. Overalll the biowheel does give the emp a slight edge in biofiltration, but the AC makes up for it with higher flow rate (AC 500) and more surface area with their sponge media. I personally run biomax in mine which gives a HUGE amount of breeding area for bacteria. Furthermore, sound is a big difference, straight from the box my emporer wa a tank, it was loud and i had to run it on the highest setting everytime to keep the noise down, if i turned it down for feeding, it sounded like it would blow up. That never changed either, no matter how many times i cleaned it. Oh and another thing, cleaning that sucker out once a months or every 2 months wasnt much fun either. The ACs are easier to clean, just gotta remember to get the little crevices in the motor. Overall strength, Emporer has the edge cuz it is thicker, but the newer AC's are pretty good and getting bettter, but unless you chuck them both against a wall u wont notice. Money wize, i believe in the states, AC's are cheaper, up here in canada, alot cheaper. Mechenical filtration is about the same, but with an AC u dont have to run their carbon. Also i did find a way to rinse the cartidges, by spraying high pressure water on them, the junk would peel off, but when i look back i lost alot of bacteria and it would just clog up faster. Also talking about flow, the Acquaclears almost always have a constant flow, you set it to its highest and thats what you'll get for years to come, over 4-5 months my Emporer didnt seem as powerful as it always was. Another point is the intake design. The emporer's is a little more friendly to smaller fish, but when ur pumpin 400 gph i think it doesnt matter. The AC has a smart design which wont allow most fish unless fish or less that an inche to get sucked up but can handle large particles for mechincal filtration. From an energy use standpoint, Acquaclear is on top, b/c the emporer uses 2 pumps or something like that, 1 for the usual filtration, 1 for the biowheels. Well thats all for now i guess, hope this helps