There are a lot of purely functional laptop bags out there. If you’re looking for that, my top recommendation is the Timbuk2 Command, which is super-sturdy and also has a neat feature that makes it easier to take through airport security. (The water bottle holder is a little small, though.)
However, if you are a professional and/or are at all vain, you might want something more formal-looking. Structured. But also, you probably want a bag with actual functioning pockets and/or organization, and maybe one that will not kill your shoulders. This post is for you!
I have not actually tried any of these bags. (Largely because right now I do not have a functioning laptop, and getting one is a higher priority than getting a bag for it!) But, as you’ll see, I have done ridiculous amounts of research into their functionality.