Depends on what you want to do, if you're doing more work related things that require more cores, like multitasking and editing/rendering the 6800k would handle it better, or if you are using the PC to play games the higher clock speed and lower price would be more viable because the extra cores aren't needed and the 7700k would be best.
Basically
Large amount of professional level work: 6800k
Anything Else: 7700k