My favorite is my 4" GP100. After several years of shooting, carrying, tuning, etc, it is nearly perfect. It goes on every camping and hunting trip. It's perfectly balanced for the type of shooting I do with it. It's not too heavy and not too light. I checked out a 686, but it didn't quite "fit" me.
Over the years, I have done the following:
Gunsmith:
Taylor Throat mod to the barrel
Recrown to 11 degrees
removed endshake
Me:
polished trigger assembly
changed springs for lighter pull
installed Hogue cocobolo grips
installed Williams firesights, then replaced the rear with a Millet after 4 years of use.
The DA trigger is smooth and light. The SA pull could use some work, but since I almost never shoot SA, I don't worry about it. The gun is "minute of pieplate" at 100yds in my hands on a good day.
I have two loads for it. The first is a 38special load that is just shy of +P with a 158gr plated FP bullet. The second is a 180gr SJHP running at 1200fps (I have gone as high as 1400). I have some 230gr wadcutters I want to work up next.
I wouldn't mind having a S&W 19 or 27, but I'd rather have my GP100 as my "work" gun.
Chris