Hardest I've done is Poison Spider Mesa in Moab, and Jenny Creek here at home. PSM was a ton of fun, amidst the difficulty, one of those "I can't believe I just rode up that" days.. but the pain factor of not making something was also a little intense.
JC was actually fun, but I lost momentum in the river a couple times and had to put a foot down. Very difficult to get going again in those mossy rocks, and I had a wet foot.
99 uzj100, gx470
05 525EXC, 01 XT225, 07 TTR90, 07 CRF50