Both great filters. I have both the emp280 and emp 400 and am partial to them because they have a seperate plastic tray that can be used for chemical(carbon filtration)or additional bio--biomax fits perfectly inside the tray. But, the ac110 does provide a bit more flow and is a little quieter. How big is your tank?
I have 2 ac110 filters on one of my 180g tanks and I have an emperor 400 on a 150g tank. Both of these brands work great!!!! If given a choice though I would recomend the ac110 over the emp 400.
AquaClear! First the media can be rinsed out for well over a year so it does not keep nickel and diming you cost wise. I personally think they are the best HOB filters.
AC110 is way better. I bought some used ones without any bio-rings. I fit 8 scrubbies in there on top of the sponge. Tons of BIo filtration. And like said earlier you don't have to replace the sponge every month. Just rinse and replace. The 400's I have had were way harder to start and noisier.