I would say there are three things to consider in order to make your decision:
1. Do you have any health issues?
2. What do you want to do with your PPL when you qualify?
3. How much cash can you spend now on learning to fly?
To take each in turn:
1. The NPPL only requires a sign-off from your GP (the standard is the same as for driving lorries) whereas the JAR PPL needs an aeromedical certificate, done by an aero doctor. This costs more (your GP will also probably charge for his signature) and the standards are higher - certainly more of you is tested! There are lots of folks flying on an NPPL who can't get or have lost a JAR PPL due to medical issues. In summary - if you have health issues, NPPL may enable you to fly where a JAR PPL wouldn't.
2. The NPPL is valid in the UK during the day. You can't add any ratings (say to fly on instruments or at night). The JAR PPL is a European licence and can be validated to fly in most countries worldwide (with varying levels of bureaucracy!). If you just intend to fly locally at the weekends on nice days, why not just have an NPPL? If you want to tour abroad (even go to France for lunch or something) or you want to learn instrument flying or night flying, better go for the JAR PPL.
3. Although the prices you mention are for completion in minimum hours, the relative expense of NPPL v JAR remains about the same. If you can't afford to spend quite as much money now, maybe you can afford the NPPL but not the JAR. If that's the case, it's pretty simple to 'upgrade' later if you want to.
One last thing - there is no such thing as a helicopter NPPL yet, so if you want to fly helos, it has to be a JAR PPL(H). As stated, you don't need a fixed wing licence first but helicopters are about double the price of fixed wings to learn on, so you need a decent-sized wallet!
You will find that most training schools teach JAR as well as NPPL - most of the lessons are the same anyway. Until quite a long way through learning to fly, you don't really have to commit yourself to either option...
Hope that helps.