Nobody has brought up that dreaded disease older guys get, Arthritis. I would think a side lever would allow you to use a gun for for longer than a top lever.

I had a discussion with Toby Barclay at the Vintagers in Rhode Island one year and he said left side levers worked better for right handed guys.

I have never used a side lever gun and have never bought one. They are relatively rare to find in good condition, especially left sided ones.

So many guns, so little time!