In choosing a paveing contractor, what should I be looking for in the warrnty's they offer?

I would look for a one year warranty specifically covering cracks, settlement/rutting or ravelling.
But more important is getting quality during the construction. First, you need a good mix from a plant that produces significant quantities of hot mix asphalt (HMA). Second, the stone base needs a good foundation with good drainage. The HMA needs to be placed hot - that is totally rolled out before it cools to 180 degrees or so.
Give him specifications for the construction, and make them part of the contract. Inspect the work while it is being done, or hire a certified inspector to do it for you. Document any failure to abide by the specs.