I picked up a soft-skinned rolling Samsonite 5 years ago, (international) cabin size. I found cabin size good for keeping the packing to a minimum, and it also makes it easy to accomplish more efficient arrivals when positioning commercially, rolling past the arriving baggage belt with an air of smugness.
Summer season packing is a no-brainer, and over the years I have come up with a winter pack that allows me to survive even the coldest Mongolian winter. I find shoes and boots to be the biggest space killer - but the biggest waste of space is the fitness gear that I pack for each and every trip...
I am a fan of the roller bag because we tend to go places where there are no FBOs, so bag-dragging through terminals and across tarmacs is a regular event. A lighter, smaller bag makes it easy to drop the bag onto a security screening conveyor, or to toss up into the baggage hold.
I also find it helpful to have a roller with a flat top to allow stacking of catering or other crew bags when there simply aren't enough hands.
The downside with my bag setup is that most travelling purchases end up in separate bags as there is no room to spare.
I am lucky to work with like-minded light travellers - so it is easy to help each other out when getting around.
Happy tray surfing!