Penguin/Emperor cartridges only clog up quickly if there is a bunch of gunk in your water that needs to be pulled out. I think the AquaClears are fine filters, but I don't think they keep water as pristine as the Marineland filters do. As for using the AquaClears, I do recommend using the setup they recommend (foam, carbon, biomax). I changed the foam once a quarter, and it wasn't really necessary even then; they rinse pretty clean. I changed the carbon monthly, though the Hagen carbon did seem to tucker out before a month. The biomax will smooth out after about a year and not be quite as hospitable of a host; I recommend there buying the Seachem Matrix already bagged, and using two of them. When it's time to change, change one and wait until the next month to change the other one. Watch out for the motor on the AC filters; sometimes they don't start back after a power outage without taking them out and cleaning them. One final suggestion before purchasing: call the Hagen help line and the Marineland help line to see what your experience will be like if you need to talk to someone.
As for where to get your filter, I would print out the PetsMart online price and have a local store honor it. It may not beat the absolute best price online, but to get close with the convenience of a b&m store earns my loyalty.