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