Hard for me to vote as I think a lot depends on the application. Planted or unplanted, how much control do you need over speeds, spraybars required...? Lots of unanswered questions. I can answer this for mysel, however: Penguins. Not as expensive or fancy as their Emperor counterparts, but I like simple and easy to clean. As others have stated, I have never had a problem with a Penguin restarting after powering down. Poof, it just works, ya know? I have a planted tank, but use Penguins with the biowheels. My CO2 supplement is Flourish Excel and it's a small tank so cost effective as well. Also, FWIW, I have cycled tanks by simply moving bio-wheels so they obviously hold enough bacteria to get the job done.