There are a number of things to consider. Will the school in the USA employ you as a CFI when you have completed your course with them? I have heard that HAI employ only one in ten of their new CFI's. I certainly get lots of resumes from CFIs who are not placed by their school. Having said that if you do get placed you should get around 1,000 hours a year from a good school.
It's all about experience and hours. As said in previous posts you are almost unemployable with low hours. If you have 1 or 2,000 hours you are very employable. All of your helo flying in the USA counts towards a JAA licence despite what some people are suggesting. The FAA licence is an ICAO licence.
Costing is of primary importance to many people. Do the UK costs include VAT, landings etc? Any extras? To suggest that it is cheaper in the UK, even after accommodation costs are included is simply not true. The J1 visa is a good opportunity to live and work in the USA gaining those valuable hours.
Finally anyone suggesting that the training in the USA is an inferior product probably have their own agenda. Don't be afraid to question the record of the school and do speak to ex-students about their experiences. Any school that does not supply that information when requested should probably be avoided.
I have operated under both systems so I feel qualified to comment. I am not hiding my interest in this subject. My website is listed on the message.
Regards,
Chopperpilot47