Bristol.GS is an ATPL theory provider only, whereas OAA provide the whole ab-intio PPL through to MCC/JOC training.
Whilst Oxford may not be 'as good as they used to be' (probably because the price increase and value of the pound to dollar), they're still placing many cadets into multiple airlines across Europe.
OAA's ATPL material versus BGS will ultimately come down to personal preference.
I'm studying using BGS ATM and I'm very happy. I have looked at OAA's and whilst the content is good, there seems to be a lot of surplus detail that doesn't need to be studied.
However, if you have all the ATPL manuals from Oxford, pick up where you left off and crack on.