LOCO's prefer to go off jetty as they can empty and board a plane much faster with 2 exits than with one.
EasyJet use contact stands now and again, usually at the bigger airports (I have used air bridges with EZY at EDI, LGW, HAM, BFS and STN), but in all my FR flights I don't think I have ever seen them using one. Most of the airports they fly to don't have jetties anyway, but the ones that do they never use them. I don't know if they are charged more, but they are certainly charged for the time they take up a stand, so anything which minimises that will win.