Fairly recently in trying to make a purchase decision, I shot the 4" 686, Ruger 101 and the 620 and went with the 620. I just shot it better (i.e. it worked best for me) than the other two. I also didn't like the feel of the 686 or the way it looked compared to the 620. Shooting identical ammo through both I didn't notice any difference in the felt recoil between the 620and 686 despite the slightly heavier 686 and the lug, but there are more experienced shooters here who probably could.

That's my .02 in favor of the 620. I just learned to sort of gather a lot of info from good sources, factor it in and then trust myself and my experience and get what I like. They're both great guns.