IMO ac's are way better for mech. But if you'll do a search on here, you'll see this thread about 100 times and it usually comes down to everyone loves emperors for bio and ac's for mech. Now with my ac's I use 2 sponges and with my emperor I put matrix in the cartridges, that may have something to do with it....on my 55 I use on of each, and on my 46 I use an ac110 and an ac70 right now. I've never really had a problem with either, but I have a friend that had some issues with her emperor. Also, for the gph compared to media space, ac wins hands down, so if you ran it with the rings or matrix instead of extra sponges it may be just as good for bio as an emperor, not sure about that.