When I was much younger, I used to ride to my summer job with backpacks.

Now I prefer panniers for their low center of gravity and to allow ventilation on my back. I don't like the trapezoidal shape of pure panniers and they are awkward when you need to carry them around. I also don't like that they are a little more than sacks so you have to rummage and mess up your packing just to look for stuff.

Then I got an Arkel combination backpack and pannier. Being a backpack, it's got lots of pockets and a big zipper that can open the main compartment all the way down.