What are the pros and cons of both?
Read here:
http://www.golfgtiforum.co.uk/index.php?topic=65779 
I will be doing journeys of around 20 miles on motorway most of the time (to and from work etc), so which would I be better suited to??
But will you be keeping your revs mainly below 3,000 rpms? (And if so, why buy a GTI?

)
I believe LL service is between 16-20,000 miles? Whereas T&D is every year or 10k miles?
Not quite correct. The LL regime is
variable - which means under the perfect operating conditions (for the LL regime), then you may be able to achieve up to 24 months or up to around 16-17k miles (20k miles is actually impossible on a petrol engine with a turbo). However, if your operation conditions are NOT suitable for the LL regime (and even if the car has been correctly coded for LL regime), then it can need a service in as little as 12 months or as little as 9,600 miles!

And this latter isn't some kind of fantasy or myth. There are many owners who have been mislead, and found a GTI on LL needs a service after 9,600 miles (and this will then cost MORE money than if it were correctly coded to T&D).
But with the T&D servicing, you are correct. The intervals are 'fixed', in so much as it will have a 'countdown' of 365 days and 10k miles - and whichever of these is reached first, then that is when the next T&D service is due.
What are the differences in costs? Which is better for the car?
Costs, well, if you are incorrectly set to LL, it can actually cost MORE than a correctly set T&D.
And without any doubt, whatsoever, T&D is clearly much better for the car. Would you rather have fresh oil every 10k miles or every 20k miles. Would you rather have your brake pads inspected every on year or two years? A bit of a 'no-brainer'.

Also, does anyone have a full schedule of when I need to get bits done to the car (if DSG)? When it needs oil changes, cambelt changes, break fluid changes, filter changes, and so on?
Bump this thread later today, and I will give a full answer. Gotta go out now.
And Mods/Admins - this thread would be better if it were moved to the maintenance + info sub-section.

Just want to get a good idea of maintenance costs 
If you are genuinely worried about the costs of maintenance, then maybe you should really re-consider if a GTI is appropriate (or any car with DSG). But if you are merely researching for budgetary reasons, then I apologise for the above comment.
