For me it's paper on the ground, memory in the air.
Me too. But there are exceptions both ways:
- Initially you will work from checklists exclusively, but during your training some things (like downwind checks) will be drilled into you to be done from memory. In the circuit, just before landing, is not the time to spend large amounts of time with your head in the cockpit.
- Emergency drills in the air should be from memory. But there's usually also a list of abnormal procedure drills. As these are less urgent you can do them from a checklist, even in the air.
- When flying a very familiar aircraft I do the ground stuff from memory too. But that's not a change that happened overnight. To build up confidence that I would not be forgetting things I sat in the aircraft, emulating a complete flight and trying to work on a logical "flow" of things to check and do. I then referred back to the checklist to see if I hadn't missed anything. Only after a few iterations and a few of these flights was I confident enough not to need the checklist at all. And still this only applies to one specific aircraft that I fly a lot. All other types I still use the checklist.