The are two options in the US:
a) an FAA PPL (which allows you to fly a G-reg worldwide but is nearly useless for other European registrations)
b) a JAA PPL (which can be done at only a few U.S. schools)
I have a standalone CAA and FAA PPLs and can say the FAA one is harder. It also includes a night rating as standard, whose flying requirements exceed that of the JAA one. I did the IR in the USA and that was very tough indeed.
However, be careful to compare like with like. If you go to the USA, you will be flying solidly until done, for say 4 weeks. If you did the same in the UK (basically, booked yourself into a B&B near the airport and flew daily; something virtually nobody does over here) you would also do the PPL in 4 weeks - assuming good weather. Instead, people slot the flying into their lives over here, and spend a leisurely year or so doing it, not to mention an average of £8k-10k.
The cost saving of US training is eaten into by airline tickets and accommodation, not to mention the significant time spent grinding through the paperwork for TSA and Visa.