Well I think that gravel is poor for soil and also hard to weed, membranes on paths tend to get covered and disappear into soil, and bark lets weeds grow through unless you use a lot. Its also a question of what you like to look at.
I have a lot of paths here and do most of the weeding myself and its not onerous at all, they have compost on top. Unless the bark is free, I would buy compost.
