I think a 3" 686 would be a great carry gun. However, everyone is different so you need to figure out if one would work for you specifically.

I prefer a larger frame. I used to carry a 2" Detective Special, which is Colt's D frame, but wanted a slightly bigger gun with more power. So I upgraded to the 2.5" Python which is on the I frame, about equal to S&W's L frame. I love the snub Python for carry, it is perfect for me, the size, the weight, the power.

Hindsight is 20/20, and if I had to do it all over again, I probably would have gotten a 4" Python instead. Would have been cheaper for starters, but would also have given me better accuracy and more velocity. I like my snubby though. A 3" Python would have been perfect, but obtaining one of those for a realistic price is unrealistic.

So a 3" 686 would work great for someone like me. In fact, I considered a 2.5" 686 but I am really anal about action design and dedicated to the Colt V spring. I would take some time to think it over and decide on what exact configuration fits your bill. An inch or so barrel difference doesn't make much difference on guns of the same frame size when it comes to carrying or concealing. So I wouldn't rule out a 4", or even 2.5" the other way.

For combat shooting, I got combat grips from Karl Nill. They are expensive, but they are one of the highest quality grips I have seen. The fit is amazing on my Python. They are designed specifically for shooters and make the gun point fantastic when combat shooting (no sights).

For holster, I just have a Bianchi Accumold right now. It was cheap and actually gives a nice high ride OWB which is concealable. The holster covers most of the gun's frame to protect it, which I require for nice guns. Eventually I plan to get a Galco or Desantis combat leather for high ride OWB carry. I go with OWB so the gun is always easy to draw, and I practice drawing and combat shooting. A carry gun isn't worth anything if you don't practice, practice, practice how to use it well.

Here's my dirty girl after some range drills.