Either will serve you well. It may come down to what is readily available in your area. If both are available I would go with the 686,(no hole). It is a bit beefier for lots of shooting.
I decided to go with the 66 in the 4" instead of the 686 4" cause it's lighter but then I have not been able to find a new one so I bought the 19 in the 4" and the store is holding it till my permit arrives, which it just did today. I hear the blue rusts more easily so should I wait for the 66 to come in or go with the 19? It is beautiful but I think I prefer the stainless steel. Anyway, hope I am making the right choice. The 686 was definitely too heavy and bulky for me.
Of the 2 you mention, I'd go with the 686 because I prefer the aesthetics of the 1 piece barrel of the current production 66. To my eye Smith's 2 piece barrels just don't have a clean, well executed look - they look cheap. Also the 686 is a real tank.