I'm not a fan of either boxing or UFC, but from what I can tell, boxers take far more headshots, while UFC fighters are hit elsewhere more, and can get other injuries -- e.g., armbars can break arms and tear ligaments (http://www.mma-training.com/arm-bar/). While I'd rather not get any longterm injuries, CTE (https://en.wikipedia.org/wiki/Chronic_traumatic_encephalopat...) is far scarier to me than most longterm effects I can think of UFC fighters getting.