I use a single Carradice pannier on my commute. The cotton canvas is pretty lightweight, water-resistant, and very resistant to abrasion. I have slid along the road twice and the pannier absorbed all the impact.
Look for a good clip-on fitting system (Ortleib is the best)
a lightweight stiffening board thet covers the floor as well as the inside wall (corrugated plastic)and plenty of reflective stuff.
I prefer one large compartment with a pocket. I also find that a flap with clips is useful if you are always diving into your bag. The Ortleib roll top is more hassle to get into, but more waterproof.
I dont think nylon/cordura is a good material for panniers, it seems to wear, and the waterproofing simply wont last.
I used to use a cheapie set of panniers, but quality ones are soo much better.