I rode with a backpack for years and never liked it much. It worked well enough, but for me, it caused discomfort in my chicken wings and a wet, nasty back from sweat.

Now that I am older, self-employed, and maintaining deteriorating knees, my days of aggressive riding and bunny-hopping are behind me. I can relax and choose a route and a pace that works for me. Rack and panniers are a much better choice.

I also use my bike for shopping and many other hauling activities, so again, the panniers make more sense for this stage of my cycling journey.

All that being said, backpacks are an excellent option if they work for your needs / system.