I have a 32 mi RT commute and have used panniers and a backpack. I prefer the backpack.

One pro for backpack you didn't mention is you can use it on any bike, and all of your bikes, even ones that don't accommodate racks. You don't have the expense of a rack and panniers.

I have a mission workshop, which is waterproof. Sure my back sweats more, but I never to Tice it really. It is just more convenient to me.