[Zeitgeist]

the reason some classes seem to get crits more often is due to the nature of the crit forumula - any class that does splash/aoe damage is going to end up getting more random crits (because they have the possibility of doing more damage per shot, therefore higher damage per second), as well as any class using a weapon with a high rate of fire (more damage per second), and any class whos attack does substantial damage per hit (more damage per shot = more damage per second provided attack speed remains constant)

for most classes that's pretty balanced out, but i think Demos not only do huge splash damage like Soldiers but they can release their ammo much quicker, and a demos secondary is far more efficient using the crit "criteria" i mentioned above

nothing too scientific or even planned or tested, but, IMO looking at it logically, the formula for random crits benefits demos the greatest.