I am VERY happy with a new rollaboard with two outside pockets, one for the laptop and one for the paperwork in a plastic envelope. Easy to grab the laptop at security, then slide it right back in.
Into my backpack goes anything I want during the flight plus all kinds of junk; I hang it on the rollaboard walking through the airport.
I find it much more comfortable to use the backpack if I ever have to actually carry my computer (or any other heavy stuff like that champagne from duty free) around. Once onboard, I’ve trained myself to grab the laptop and paperwork, stuff them into the backpack and put it under the seat in front of me before I throw the rollaboard up in the overhead.