Earthswater, i have owned emperor 400, and penguin 350 from marineland as well as a few canisters from them.
IMO they are pretty good filters but the AC are far superior. If you do go with an emperor 400 i would suggest you buy a bulk roll of polyfiber and cut some pieces to fit. On my penguin 350 i currently have 1 of the filter pads for the canister and 2 polyfiber pads behind it. The polyfiber catches smaller particles than the filters that come with the emperor/penguin series and is a must have IMO. These filters are not bad, but the canister design of the Aquaclear is far superior.
The Aquaclear is alot easier to clean as well and with the huge sponge that it brings you barely even have to clean it compared to the marinelands!
here a link on ebay to a new AC110 with free shipping for $63.
http://cgi.ebay.com/AquaClear-110-A...ltDomain_0&hash=item483d6b5ab9#ht_2661wt_1269
You cant go wrong with that