Polyester(Dacron) is bester[I'm sorry].
Nylon(non-aromatic polyamide) is broken down by UV quite quickly, polyester is quite resistant to UV. Both are very chemical resistant. They have very similar breaking strength, but PE hardly stretches (sometimes good) and Nylon will nearly double in length before it breaks (other times good, a bit like a bungee cord). Coatings can give Nylon moderate UV resistance but they ware off eventually).
I haven't looked up much on it quite yet but acrylic fabric like Sunbrella is supposed to be UV proof, like polyester.
Wax/oil soaked cotton/hemp is waterproof tough and UV proof. It is heavier though at 12-24oz per square yard for bag-luggage thickness, verses 6-11oz(400-1000denier packcloth) for nylon or polyester.

For compairson 1-2oz nylon is for sleeping bags, and light tents. 200d (3.5-4oz) nylon is for stuff sacks. 330d is light packcloth and for stuffsacks 430d(7oz) is standard tough hiking backpack cloth. 1050d (16oz) ballistic weave(a course thick weave) is for the burliest soft side luggage. 1000d oxford(a flatter standard weave) (11oz) is used on soft luggage.
Synthetics are generally measured in denier and natural fabrics in ounces per square yard. Denier is the weight/thickness of the thread used to weave the fabric.

I know a bit more about fabric if you all would like to know, I'm no bonified expert but I have done a bit of research.