It would seem GV+ jobs pay the best. BBJ and ACJ coming in close behind.
The reason there are so many Boeing drivers around is because there are so many Boeings!
The reason that there are so few jobs on BBJs is because there aren't actually that many BBJs, and those that have a job on a true VIP BBJ tend to hang on to their positions for a while, and it is a very small community.
There is a big difference between VIP BBJ, and corporate Boeing business jets.
To be given an 'in' to the private jet world on any of a companies operating type is unheard of. Friends in high places you must have!
Good luck.