Best method of shed foundations? slabs or concrete?

For me, the concrete foundation is probably the easiest to get completely even. I have done one in the last year, and used paving slabs, but my reason is that I live in a mid-terrace house, so it was easier to bring in slabs and sand than try to get wheelbarrows in through the house. So, if access isn't a problem, maybe the concrete option. As for the longevity, I imagine that they would last the same amount of time if done right.
now that's my tuppence worth, hope that helps
Wheelo

lay your slabs on a good compo base ( sand and cement ) and will last a lot longer that your shed ever will

ive got a metal shed next size up and used concrete base (i already had a mixer) and that was quicker/easier than it was to put slabs down for my greenhouse