Since you will have bags, I feel compelled to advise you that you will end up lugging them twice (more than the taxi alone) if you go the taxi + Maglev route: 1) from the taxi to the train; and 2) from the train to terminal 1 or terminal 2. Neither of these walks are especially taxing, and you get use luggage carts at PVG, but the taxi is certainly more convenient in this regard (drops off within 100 meters of the check-in counters). As for the bus, People's Square is a huge place, and I can't recall from where it departs off the top of my head.