I am not and never have studied at BGS or OAA, but I am studying from the Bristol material (CBT and books). So far I can tell that the explanation is pretty poor and sometimes you have to read the same boring stuff a million times and do a lot of research in other places to get your answer (or alternatively ask the instructor, but I choose this as a last resort). It is hard to do the tests as well because often There are quite a few noticeable mistakes as well, nobody's perfect, but these are big ones.
I haven't compared it to OAA, and can't say that I am unhappy with them, but I imagine things could be done a bit easier and clearer. I've heard similar things from our instructors as well.
Anyway, the guys are right, either will get you there, one will be cheaper, one will be a bit easier and more informative, but again, both will get you there.