You have a mixture of instructors, American, British, European, old and young. They have all been through an Oxford standards course so in Theory the training you receive should be the same no matter who you get as an instructor. The main problem - and again I can only comment through personal experience - was with 1 American instructor whom from what I was told, didnt teach "the Oxford way''.
Hmm, what else can I tell you....... ahh, very important, Texan girls are georgous!!!
I would go with Oxford if I were you, I have had very little problems (so far) with them and the training is excellent.