Forty litres, no checked bag, and no argument at the gate.

Why it earns its carry-on spot
Forty litres is the sweet spot for anyone trying to travel without checking a bag. It’s enough for a week if you pack with any discipline at all, and small enough to stay in the overhead locker rather than disappearing into the hold for an hour at the other end.
The hard shell does the work that soft luggage can’t, protecting whatever you’ve wedged in around the edges when the case gets thrown a little bit. Wheels and a proper handle matter more than people account for on a long walk through a terminal. Always worth checking your airline’s cabin dimensions before you fly, since the limits vary more than they should.
WHO PACKS THIS
For the traveller who has decided that waiting at baggage reclaim is optional.
The Carry-On Only Convert: She’s timed how long reclaim takes and decided against it permanently. This is the bag that makes that workable for a full week.
The Weekend City Breaker: Two nights, one bag, straight out of the airport and into the city. No waiting around at the other end.
The Business Traveller: Overnight trips where the whole point is speed. A hard shell also keeps a suit in better condition than a soft holdall.
The Nervous Packer: Losing a checked bag ruins a trip. Keeping everything with you removes that possibility entirely.
