I've never heard of Mammoth but don't go by me because there may be a lot of brands I haven't heard of. I definitely like the looks of the Trek better if that means anything. I will agree that the Mammoth has Deore drivetrain vs Altus on the Trek so it should be better in theory. Everything else seems to be tit-for-tat. Something else that might make a difference is would you rather have 1x10 or is 2x8 OK?