I like 4 - 7.5" because of ballistics, handling and accuracy.
I have a 5.5" Ruger SA. It is easy for me to hit with out to 50 yards, but 75 is reaching. I used to shoot a 10.5" 44 mag and killed a deer at 125 yds, so a lot is in the barrel length and sights.
To me, 5.5" is a great packing/hunting length. With practice, my 100 yard shooting should get better!
If it was more of a pure hunting gun, I would like 7.5" better.
If more of a SD Bear stopper, I think 4" would be ideal as 4" is about as long as you can sit in a car with in a normal holster.