From a filtration basics perspective, I find the AC filters are superior to the QF filters. You want your water to get through a significant amount of surface on the media for mechanical filtration, and you want your water to flow slowly through as much media as possible for chemical/biological filtration to happen.
In the AC, this happens because the water is flowing vertically up the media canister through the different media before leaving the filter. Obviously water does leak around edges of the media holder and skips some of the media... but throw in some java moss through the filter and you'll see it disperse relatively evenly through the bottom of the media.
In my short experience with the QF filters, the water flows horizontally from back to front, through a thin "cartridge" that has a lot of surface area for mechanical filtration, but very little depth for chemical/biological filtration. My other qualm with these is that water flow seems to concentrate around the height of the water level. Again, throw some java moss and see the pattern that emerges. (a small oval around the height of the outflow.) That means that not all that surface area is really being used.
QF media is thin:
All that said, the real reason I switched from QF to AC is that I kept breaking the QF filter intakes while trying to cover them with tight fitting foam, and AC replacement parts were more readily available. (Blame it on my brute strength!) Then again, if I was looking for a temporary backup filter, the QF would do just fine (I keep one in the closet for that purpose). I do love the self priming aspect of the QF and wish the AC did something similar. I also find their impeller setup to be more reliable than the AC (less clogging), probably because of how it is laid out in the intake.