For bsnes, accurate uses more resources to emulate more accurately. Some emulators aren't as accurate. They aren't exactly 1-to-1 compared to SNES. That doesn't mean they perform worse. In fact, it often means they perform better. But running better (or different in any way) means it's a less accurate emulation. The other versions of bsnes and snes9x are less accurate emulators, but require less resources.

From a practical standpoint, I'm not sure you'd even notice the difference between any of them. Snes9x takes significantly less resources than bsnes though. Unless accuracy is what you care about snes9x is the better option.