I like the APC 15x6 on my 91FZ in the UCD. I tried the APC 16x6 and 16x4w. The larger ones had more torque and it was harder to hold a straight hover. The 15x6 spins up faster and seems to pull out of the hover better to me. The 16x4w made a loud high pitched scream and was kind of annoying.

Chris