CFS stands for Completely Fair Scheduler
BFS stands for Brain **** Scheduler
Basically, CFS is going to spread the wealth with your processing power. BFS is going to favor giving more juice to your foreground process. So it might be better for gaming and stuff.
I have used both, and CFS is a little smoother on my phone, and a little easier on the battery. I think that some phones are not quite as accepting of BFS kernels, but really the only way to figure it out is to try. With any kernel, your phone's reaction to it will be different than my phone's reaction to the same kernel, so flash away.
What ROM are you running? Some kernels are for sense and some are for AOSP. You need to make sure you flash the right kind of kernel for the ROM you are running.