Fixed.
I mostly hunt elk with archery equipment. A fixed blade is durable, fail safe, and can be plenty accurate.
Year's ago I tried mechanical. I shot the biggest bull I've ever launched an arrow at in the shoulder. Granted, I should not have put it in his shoulder, but that broadhead exploded like it hit a brick wall and bounced right out. The furule was bent about 80 degrees and all the blades were missing. I watched the bull cross the draw and continue to bugle without so much as a limp.
The following year I switched to the G5 Montec, when they were first released. I shot a 6x6 bull, though a much smaller bull, and the Montec blew right thru both shoulderblades. Only differences in setup was the broadhead, and the size of the bull.