From a practical standpoint, unless you live in the US, for a US one you'll be on a course, and the course will be a fixed time period.
So, putting aside cost for the moment, you can either do it in 5-6 weeks in the US, with a reasonable guarantee of the weather being suitable 80% of the time or you *can* do the same in the UK, but it depends on the weather far more.
If you can't take the time to do it on a concentrated course in either the UK or US, it takes on average around 18 months in the UK if you're working full time and doing 1-2 hours a week.
Questions you should think about are:
- how long do I have to do it, how long do you want it to take?
- can I take 5 weeks off work for concentrated course (either here or in the US)
- can you actually take 5 weeks off in the UK without distraction?
- if you can take 5 weeks off, when can you do it (because that makes the US a better bet unless you're doing it in summer in the UK)
- what do you want to do with it in the future?
Flying the US/UK is not that different - there's plenty of inclement weather in the US especially around November in FL. Cessnas are perfectly fine to train in, and there's no point training in a Garmin G1000 glass rocketship if you can only rent steam gauge spam cans once you get the ticket.
The US *can* be cheaper - depending where you live. For example, in Aberdeen it's £20 per touch/landing, and £200 per hour - I cut my costs by 50% by going to the US - but Aberdeen is an extreem example, with no proper training provision (until recently) and the most expensive Avgas in the UK. It may be that by the time you factor in travel/accomo, the US = UK - but again, the benefit is you're away from the UK focused on a single task in a single minded environment with your peers who are there for the same thing.
It depends largely on your own preference. I went to the US due to cost, and because I'd have never got away from the work phone if I'd done it in the UK - concentrated course or not. Taking my self to the US, focused on only one thing, and getting flyable weather 80% of the time meant I could concentrate on the learning and flying - and the continual flying consistency really improves your skills versus 1 lesson a week.
Horses for courses. If you do go to the US - heed the advice and get an FAA ticket at the same time as a JAA one. And do the exams BEFORE you go (maybe with the exception of Nav which is easier once you're actually doing cross countries).
I absolutely loved doing my PPL at OBA - it was 5 weeks of pure day-in-day out aviation, with only 2 nights out towards the end. You ate-slept-did flying 24/7 - excellent fun!
And whatever you do - NEVER PAY UP FRONT!