I like a rack with wald folding baskets and a bungee cargo net into which I throw my backpack. Not the most elegant looking of solutions, but it's like 10 seconds on each end, is super easy to carry the backpack to where I go changed and, if I decide to get groceries on the way home, the backpack can go on my back and the groceries can fill the baskets. Downsides, heavy, not particularly attractive. But, if you're using a dedicated commuter, it's not such a big deal.