Hi Kimmer......really it all depends on what type of garden you want,,,how large it is and how you are going to use it. If I were you I would draw the area and put in place all the areas you need and work round them. You have to take into consideration too which way it faces for any planting.

cheaper and nicer dont tend to go together in my experience. personally go for nicer rather than cheapest. that way you are more likely to be happier longer.

The other thing to consider is the area itself - if its shady, the slabs will need pressure washing every spring and may become slimy in the winter, if its under trees, pea shingle will get covered in leaves in the autumn.

plus remember when laying shingle cats like to do their number twos in it .we had that problem

I had a problem with bark, It became a lovely home for loads of insects and they all came out to bite me in the evenings! I wanted 'labour-saving' but I've gone back to grass. It looks prettier too.
Bark rots down and will need to be replaced regularly.

You're right Seabird, it does rot down, but takes a good couple of years or more, and enriches the soil as it does so. Personally, I'd go for plants as groundcover!