slab flooring or stumps?

What are peoples opinion on extensions floorings in regards to wooden stumps or slab?
I am about to extend, i have wooden floors and they all have floor coverings.
And i was just going to go with the flooring sheets, as i thought this maybe the cheapest and easiest way.
Now i am having thoughts on a concrete floor.

Thoughts?

A timber floor is far easier on the legs than a slab.
Plus you can varnish a timber floor , even sheet lookks ok with varnish.
With a slab you must use floor coverings