Nothing wrong with the guns you mentioned, all (686,GP100, M28) are great, but not great CCW guns.
Since you don't have the gun yet why not go with the S&W 66. The S&W 66 comes in a 4 inch barrel, has the same grip as the 686, but is slightly smaller and lighter than the three you mentioned. Its better, but still not great as a CCW revolver (the 2 1/2 inch version is great).
However, they were the police standard for a combat weapon for many years. Even though there are alot of great defense weapons out there now, that doesn't take away or deminish the M66's capabilities. There are a ton of them out there and can be found at reasonable prices.