It depends how much time you can devote to it.
If you're able to get a full month off, you'd be just as well doing it in Scotland. The key thing would be to get all the ground exams out of the way before you started the practical flying. This can be done at home, for free, with the books, and just take the exams when you're ready. Then take the time off and hit the flying course hard in Scotland.
Otherwise, you start the flight training, and your practical flying gets way ahead of your groundschool. Typically a school will not send you first solo until you have air law, will not send you solo nav without the nav exam and possibly Met and Comms, and by law you cannot take your practical test until you have completed all 7 written exams.
Once you have your licence, if you are planning to fly in Scotland, I would just get the licence in Scotland. If you get a USA licence, any money you save will simply be spent at a flying school in Scotland getting used to the local area/radio/airspace stuff. May aswell just do it here from day one.