In reply to PPP:
Just a honest guestion, but Why so big?
what are you carrying on top of the laptop, charger etc.?
if not much, then a messenger bag kind of thing will work. Less so, If you like to take with ya everything and the sink.
For rucksacks, I recall Osprey has had some good ones (more function and less style a’la Riisto’Ryx).
last resort is What ever backpack and a laptop-sleeve inside the main compartment.