hm, i would take an emperor over a comparable AC *any day*. for me, the ACs have a real major problem restarting. they just will not prime correctly. the slightest power surge (and i live in FL, so they happen quite a bit!), and i have to poke at the impeller to get it restarted. very annoying. otherwise, it's a quality filter with a lot of media space. the emperor in my opinion is a superior product--never jams up, never has a problem re-priming after a power surge or brief power outtage, decent media area. i can run my emp400 with basically zero maintenance for months without any problems. i run a couple penguins as well, and they are unsuprisingly cheap versions of emperors in many ways. they aren't as bad as ACs at self-priming, but they do stop up more often, you can't regulate the flow, and they seem to be quite a bit louder than emperors or ACs.