It depends on your rock work? Are you going to use a canopy or keep is clean looking with one or two fixtures in the open? For a clean look, either would work, but if you're using a canopy, I would use two 360x's and a couple LED bars to "fill" the whole tank. If you're sticking to just sofies, I think two 360x's will give you more flexibility in filling the tank, as the ap9x is fixed in it's coverage. I love Kessil's and use them on all of my tanks, but you could easily cover the tank with a couple LED bars (Quanta Pro's are my choice) and use one 360x in the middle? As you can see, there are a million ways to do this.