10yrs at British Midland and working for BA makes you realise what a tin pot unprofessional outfit they are. I was very senior and then making the jump gave me a stable roster choice over my days off,respected , looked after , much better terms and conditions, more money, better hotels in better locations,better options for transfering around other depts and other fleets.
As for the pros of staying/joining Bmi let me think er er er er er none.