Whilst not wishing to denigrate hours building in the US, I must take issue with VisaGeeza. Having flown at least 5 hours (probably nearer 50 hrs) in each of 49 states (never did make it to HI) I can confirm that the ATC environment in Europe is significantly more intense and entirely different.
On the other hand, crosswinds and changing environments are far more significant in some parts of the US than anywhere in Europe - try anywhere in Colorado about now!
If you are looking to do CPL/IR in Europe, my advice would be to do at least some of your hours building in Europe but, if you have the chance to do some in the US, avoid the benign areas like FL, CA, AZ, etc - go somewhere more challenging.