If there's any lesson to be learned here, it's that the panniers vs. backpack issue is a highly personal one and it will really boil down to which one you prefer. I've gone both ways, but mostly have used a backpack in recent years due to it being much simpler for a multimode commute. My commute by bike runs between 10 and 19 miles, and the backpack is light enough that it only becomes uncomfortable in unusually warm weather or when wearing heavy rain gear. I'm also quite small and find it much easier to carry my bikes when there isn't extra weight on them.