Pros and cons with each.

Slabs are heavy to lift and take much longer to lay
Decking is cheaper but gets very slippery in winter

If i had the choice, it would be slabs every time (and i have both)

Any local landscaping company can advise

There are plenty of garden design books available or search the web for "garden design" images of what you would like.
A good starting point on the Internet that I like is http://uktv.co.uk/home/dgiped/kw/185

You could see if there any books on garden design in your local library as well.

There's been some discussion recently about the problem of rats under decking, which might influence your choice! Also decking needs maintenance whereas slabs just need sweeping and the occasional wash.

If you are asking about more than the patio its a good idea to decide first what you want of the garden - labour saving, flowers, lawn, veg, privacy etc before you start. Also consider where and when it gets sun and shade and what sort of soil you have, light/heavy, acid/alkaline.