I've been with a few DEC,BSM,AA,RED and three independent guys and I passed my test first time, 1 minor with my AA instructor. I don't think the company matters, its more about the instructor. I will say though that my red instructor taught me confidence(made me just do it) and my AA instructor was the most patient and if you paid cash it was cheaper £20.
I dropped the independent guys because they would take calls during lessons or make me stop so they could smoke, cancel my lessons or come late for lessons and not make the time up, never experienced that with RED/BSM/AA. Red/BSM were to expensive,DEC instructor english was her second language and she couldn't explain things to me properly.
Saying that I think all companies will try and squeeze more money out of you. Try and go with someone recommended by friends or family and don't buy bulk lessons until you've had 1-2 lessons with the instructor and you know you like them.