I have no idea what airline's prefer as i'm an employee not an employer, however for a CPL course it's almost a false economy to do it abroad as it's only a 25hr course.
I did it quicker and cheaper then my friends did at a US JAR FTO, because I didn't have to pay for flights and visa's to the US, the accomodation in B&B's was cheaper then rent in the US, (I paid £10 a night with evening meal!) there were no hidden registration or mystery fuel surcharge costs, I didn't need to rent or buy a car (public transport is nearly non existent in alot of the US). Very importantly you have some sort of legal protection in the UK because you are dealing with UK companies. Trust me this is very important if you feel ripped off/wronged in any way.
I recommend BCFT in Bournemouth.
I flew with a friend who did most of his flying in the US, in the south east/west region of the UK and he was utterly lost with the airspace, MATZ etc.