I'd go with FM (Shanghai Airlines) on that route because I find the service a little better than CA/MU (and much better than the lower tier airlines) plus noone flies big planes to Chengdu (I always take the CA 744 whenever offered). All that said, price should be the most important consideration. Chances are, if you book within 2 or 3 days of your flight, the better discounts (40 or 50%) will only be available on several flights. PVG is usually easier to book than SHA, but is less convenient from just about every part of Shanghai; therefore SHA flights are usually worth an extra Y100 or so IMO.