Lots of great comments. I don't own any more "L frames" . . . selling off even my limited Performance Center 646 racegun that S&W made back in 2001.
For ME, when shooting competitions I discovered that the K frames pointed and balanced perfectly, which allowed faster times between double action shots against the clock.
The "L" frames added more mass but this also required that the frame be a little taller . . . thus raising the bore axis higher above the grip, which increases the flip and recoil factor a little. S&W compensated by adding the weight of a full-underlugged barrel on 686.
As others have said en mass, the K frame is perfection in the hands.
I'll never buy a 581/586/681/686 again . . . but a nice K frame? In a heartbeat!
Wish you could fire both specimens and see what you like more.
BTW, if you want a great looking 686, find a nice 586 . . . it is the bright blued version! And, if you want a K frame Model 19 .357 in stainless, that version is called the Model 66.