I have a UK and a US ATPL and so I know what I am talking about!
I have completed the training in the US as well as in England for an ATPL licence / license.
I spent 3 years in America and I passed every single exam first time, from PPL thru to ATPL, whether it was a ground exam or flight exam.
In the UK, I failed most of my exams first time round.
This shows the level of difficulty and the standards required by each country.
Most people would think that the flying remains the same where ever you train.
I can tell you from experience that even flight training in the UK is more stringent than in the US.
As for the knowledge required, the UK ATPL demands much more knowledge that you can imagine. This could possibly prepare the pilot for any contingencies.
For e.g. : A PPL pilot got lost. An Airline Pilot started to question him about his position with regards to the sun and the ocean. Eventually, the airline pilot fixed his position and relayed the info to the rescue team. The PPL pilot was found. The Airline Pilot had utilised some of the knowledge which we learn in the UK ATPL Navs. I would imagine that 98% of American Pilots wouldn't have a clue with regards to cosmic navigation.
All areas of flying and studying including ETA's, R/T Procedures, Rules and Regulations are far more stringent in the UK than the US. This makes for a harder life but it also makes for a thoroughly well prepared Pilot. [The Creme de la Creme - The Bees Knees - The Dogs Bo!!ocks!].
Having said that, since there are less restrictions in the US, flying is more fun and relaxed.
Now the choice is up to the individual - Would u rather be relaxed or would u rather be well prepared?
I leave it up to you.