i have both a laptop pannier (axiom transition) and a deuter race exp air backpack. depending on the mood and the weather i will use one or the other, but find both are quite comfortable. the deuter has a suspension back that raises the bag off the body. there is a mesh but that allows air to circulate between the back and the bag.
with the laptop pannier, i also use the narrower axiom streamliner rack which is only about 2 inches wide so it keeps the pannier bag quite close to the center of the bike.