No contest, emperor 400 is the emperor of all HOBs. The bio wheels work great with the spray bars for oxygenation and the two extra slots in the back for chemical or extra bio is unbeatable. Also I made clamshells instead of filter cartridges and I put my own mechanical media in it with 100 micron filter pad behind it. Had Acs and they were crap with how the mechanical and chemical media was in them. My emperors are 12 yrs old and never replaced a part.