I've always preferred using backpacks to wheeled luggage, and had previously just used anything from daypack to backpacking-style bags. It was time to upgrade, and I looked at the Carry On 2.0, Tortuga Outbreaker, Peak Design Travel Backpack, and Aer Travel Pack 2.
Here's the deal: if you're paying $300 for a travel backpack, they're basically all good. Of these, though, the Minaal Carry On 2.0 was the best for me: many bags in this class visually look too big (i.e., not stealth at all), aren't great looking, and are missing features that the Carry On 2.0 has.
It's big enough for a week's worth of travel for me (including in cold climates where I'm bringing layers), and still has great access to "daily" items like laptops, keys, wallet, etc. The included rain cover saved me once, as well. It looks clean, easy to sling around, and built well.
When flying, it's fantastic. The fairly large top pockets means I can dump my pockets for TSA Security in 5 seconds, and the two chamber design lets me separate things I need for the flight vs can go in overhead storage. It also squeezes into otherwise-already-full overhead storage, and would even fit under the seat in a pinch.
Grab their packing cubes with it — super lightweight, are built well, and fit perfectly in the large chamber.