Backpack vs panniers vs rack bag vs handlebar bag vs...
I've been through the four options, and am currently on "backpack" for the second time, about to head to "rack bag" for the second time.
Most inconvenient thing about backpack, surprisingly, is that you can't remove a jacket while wearing it. I almost always start the commute with jacket on, and want to remove it after 10 mins.
Haven't found the benefits of racklessness to outweigh the inconvenience factor.
(Maybe I should give "handlebar bag" another go...)
Steve