I was curious about this too, so I decided to simulate it. It's a fun problem to model and code, with some entertaining places to trip up - for example, that brief awkward period where the elevator is full, but newly arriving people recognize they should not press the button until it leaves. In any case, the answer varies based on the rate of arrival - in some regions of the parameter space it's better if all elevators stop everywhere (intuitively, if odd people arrive every 2 min and it takes 3 min to go up and down, it becomes too expensive to have to wait for the odd elevator). But even in cases where interleaved floors performs better than all floors, there's a solution which is even better there - lower half of the floors on one elevator and the upper half (plus ground floor) on the other. This will make for a fun interactive notebook.