I have AC 70 and 20 and two Aqueon 30s! I've sold the all of them except the 70. IMHO, Aqueons are great since they have good flow rate and don't have any room for bypass while the ACs leave a tiny space. Cartridges for Aqueon are cheap on Amazon but everytime you change them, except some instability in your tank. The "bio-holster cartridge" thing is just a gimmick, and so is the 4th stage wet-dry "super oxygenation" thing. I like my ACs. The plastic is cheaper than the Aqueon, and my lids never fit right, but they're quieter and the media is a lot more flexible.
My .02!