I am leaning towards the Emperor 400 for the following:
1-it has a biowheel, and I like these
2-it's bigger than the 280-bigger =better!
Most people on this board like the AC's, but I used one and thought the design was cheap. I did like the flow control though, but I don't know if there is a control on the Emperor. I do have x2 running Penguin's using the biowheel and I like the fact that when you don't see the wheel spinning you know it's time to clean the media. You can also add ceramic media to the Emperor, just need to bag it.
G/L