What you have to remember is that most of the FAA-only places in the US are not geared for foreigners and cannot issue the I-20 that you need to get the visa. There are some exceptions but not that many.
Not all the JAA places have poor reputations. I don't want to say that you should go to one place or the other but I have flown in US before and I can confidently say that there are good JAA schools. Like I said before, the only FAA rating that is worth getting to use for conversion is the IR but if you want to do this in one trip you will need to sit both PPL tests as the CAA don't issue Temporary Airman Certificates.
One other thing that you might want to consider is the difference between Part 61 and Part 141 schools. It doesn't make much difference at PPL but there is a big difference with the IR in that under 141 you don't need the 50 hrs X-country PIC time. The definition of X-country is very different in the US from what it is here.