For me, it's XC for the sheer effort required to succeed at it, although weirdly it's the discipline I have the least interest in despite it being nearly all the actual riding I do. On DH, I like Warner's view - You only have to hang on for three minutes, how hard can it be? ?
Hardline is an outlier in terms of the outright lunacy of the features & an invitational, so I'm not sure you can read too much into it as an event to sort the men from the boys, you could argue BK had a distinct advantage this year as the guy who got to ride it a week before anyone else & a comparatively weak field what with Covid disruption & Gee being out.
Rampage leaves me cold, I find slopestyle stuff a bit dull in general but I reckon XC is pure competition, the best athlete generally wins.