Yeah, good point you bring up there coolie. Skill level plays a large par as does type of track.
All in all, from my experience I find the bigger bikes a bit easier as the suspension seems to be more forgiving, and the 'on tap' power really help to make last second judgement calls.
With the smaller bike I am finding my lower back takes more of a pounding with bumps, and you really have to make sure you're looking ahead to keep and commit a lot earlier to jumps etc to maintain enough speed and 'flow' to make jump if it is a decent size. There isnt enough power with smaller bikes to make a big jump with a small run up.
Having said that, even if a bigger bike doesnt feel the bumps as much, and has more instantaneous power, that can be a bad thing in the hands of a less experienced rider.
That's my two cents...