The best protection you can buy is to buy a quality leather to begin with. A good quality leather does not need any protection and neither is it recommended. All you will need to do is keep it cleaned= vacuum and/or wipe with a lightly damped cloth with a tiny amount of detergent. Also keep the leather away from direct sunlight, fireplaces and heating vents.

Can anyone provide a direct answer to the question? What is the best leather sofa protection product in the marke

Check this link. www.myfurnitureforum.com.
I'm having a senior moment (lol) and can't remember the man's name but he used to respond to this forum. Maybe Duane. But anyhow he says you should protect your quality leather furniture to maximize its life.

I don't know if it is the best, but I use triple crown. It is made for restoring antique leather books, which is what I originally bought it for. It is rather expensive, but goes a long way, it will darken the leather, but gives a great patina.