Hi and welcome NK,
Unfortunately, there are no definitive answers to the questions you pose. You will get proponents and detractors for both methods i.e. Europe or USA. The reasons to choose the USA have historically been to do with cost ( lower fuel prices and the weakness of the dollar) and faster training due to more favourable weather conditions.
You mention FAA training and converting on return to UK but I presume you know that you also have the option to do JAR training up to CPL/ME at approved FTO's in the USA, Naples Air Center and EFT to mention two that I know of.The Instrument rating skills test has to be completed in a JAR State so some who do a lot of their training in the USA will complete the Instrument Rating in Europe or do a 15 hour minimum conversion course to convert an FAA IR.
As to which route to take? you will have to decide for yourself. However my own son and many others I know of have done some of their training in the USA and it has not been mentioned as a problem by prospective employers.
Regards
Willby