Kempus - to try to give you unbiassed advice is tricky, but I'll try. A search for threads on PPL training in the Private Flying forum is a useful start (there are LOTS!).
Working in no particular order around the country (discounting Carlisle, but it is an option, if you wish):
Glasgow: Mix it with the big traffic, but may cause delays and cost more as a result of taxi delays, etc. Circuits can be difficult at busy times due to commercial traffic.
Edinburgh: Refer to Glasgow!
Prestwick: Many of the forum regulars have recommended it. Gives the 'Big airport' and RT / navaid experience without being too busy. May be a bit of a drive for you.
Cumbernauld: Is OK (I have a friend who is doing PPL(H) training there), but a bit restricted on facilities / runway options in the event of strong crosswinds.
Inverness: Refer to Prestwick!
Moray Flying Club: Operates out of RAF Kinloss. Moderately cheap, but instructor availability may be an issue for you as many have real jobs flying for Her Majesty!
Fife (Glenrothes): I have flown from there a few times and it's OK, but a bit restricted on runway options in the event of strong crosswinds. Good facilities and quite friendly.
Dundee: Have heard reasonable reports on it but never been there myself. Good facilities and full ATC, so good practice for RT and mixing it with the commercials.
Perth: I fly from there myself. A nice friendly atmosphere. No commercial traffic and only A/G ATC, so you may not get the practice of mixing with commercials. Tayside Aviation operate out of Perth / Dundee / Fife, so you will get used to operating at all 3.
That is all the significant training airfields in Scotland that I can think of. The question of whether to train in US or UK is always hotly debated here and there is no 'right' answer - it has to be what suits you best. If family / home / business distractions mean that it's better for you to go right away from it all and train in a 3 - 4 week block, then that's fine. USA is an option, but so is England / Jersey / South Africa / Cyprus and a lot of other places.
I have no commercial interest in this, but my sentiment leans towards training somewhere close to where you are most likely to be flying. IMHO, it is worth getting to know your home flying area extremely well, so that if you get caught out any time, you know the area intimately enough to know all the features / hazards. This is not an exam question and many others will differ with me. There is a often financial benefit in the direct training costs elsewhere, which should be offset by any costs of converting once you come back to UK to get used to UK procedures / Air Traffic / your local flying area / the UK weather. If you want to look at the time abroad as an extended working holiday, from which you return with a PPL (a licence to continue learning!), then that's fine!
I personally did around half my training in Canada (as I happened to be working out there at the time!) and came back to UK to complete, so I tend to have a hybrid view!
Whatever happens, try out a few of your local training facilities with a trial flight and see how you feel you fit in before you throw great wodges of dosh at them. If you decide to go towards the US, then check out various threads relating to Visa requirements as a result of 11 Sep 01. Buy a few flying magazines and see what the options are. As you seem to have commercial aspirations, may be worth getting a Class 1 medical done early on to see whether you are even in with a chance before you throw wodges of money into the training.
Sorry - rambled on enough here, but hopefully have covered a few of your questions.
[edited to reduce the number of typos!]