This must be a personal preference based on ear anatomy.

The first-gen Airpods fit my ears perfectly, and were secure. When I lost them and upgraded to the 2nd gen, I was initially upset - aside from the body being fatter (and so less comfortable in my ears) they were very insecure - I couldn't even walk around without them loosening and dislodging.

I was on the point of returning them when I saw the advice online to 'twist' them into a different position. I now use them with the stalks horizontal, and they're secure. Still a touch less comfortable than the v1s, but easily tolerable.