I own one AquaClear 50, two Fluval C3's and one FluvalC4. The Fluval C series is the latest technology makes the "1978" technology of the AquaClear practically an obsolete relic. Both are made by Hagen and even use the same motor up through sizes AC70 and Fluval C4.
The AquaClears are only three stage filtration with no polishing pad or trickle chamber. AquaClear suffers from severe bypass issues (just google it) or go here:
http://www.aquariumadvice.com/forums/f60/aquaclear-bypass-issues-292796.html
The only way the AC works half decent is to use tightly packed floss because the "sponge" is so coarse is lets the fine particles right on through.
I find it easier to use custom media in my Fluval C's than aquaclears because the media basket is a mess.
Here is a link to my HOB filtration section on photobucket which shows both including the use of custom media. Click on each picture for a full explanation of what you are looking at.
HOB Filtration Photos by Paul1792 | Photobucket
Also, see posts 4, 5 & 21 here:
http://www.aquariumadvice.com/forums/f60/aquaclear-vs-fluval-315148.html