As VisaGeeze says, at PPL stage it doesnt really matter if you do JAA or FAA. You can still fly in the respective countries subject to certain conditions being met.
Some schools in the UK will try and con you by saying that if you trained in the US and hold an FAA PPL then you will require 10-15 hours training on your return - my advice is run a mile, they are just after your money. I did 2 checkouts at different clubs (White Waltham & Bournemouth) and was signed off at both after an hours checkout.
You question doesnt actually say what you intend to do after your PPL though, are you going on up the ranks via the JAA or FAA route of just stopping at the PPL?
Julian.