I would choose the 4” GP100 that is shown in my avatar image, at the left side of this post. It was made in the very early Nineties, when Ruger still cared enough to machine grooves under the extractor, to accommodate some amount of unburned powder debris. The original-pattern GP100 factory grip is a perfect fit, in my hand, making the weapon “point naturally” in my hands, and the reach to the trigger face is also a perfect fit. These factors mean that a sight picture is mere confirmation of the point of aim, rather than just the beginning of an effort to align the weapon with the target.
I have fired this GP100 at much faster than the necessary speed, on a timed qual course, with scored targets. Making clanging noises on steel is fun, as is plinking at pine cones, but seeing one’s shot placement on anatomical targets, with scoring rings, is quantifiable confirmation that one can perform under time pressure.
I fired a defensive shot, into a real-life opponent, with this GP100, in the early Nineties, when this was my primary duty weapon. I do not need to depend upon what anyone has written, about the effectiveness of any particular defensive cartridge.
In 1997, I put all of my medium and large revolvers into the safe, to concentrate on the 1911 trigger system. I used 1911 pistols for police duty, and personal-time carry, and used a small-J-Frame only as a secondary weapon. My training with that J-Frame was rather minimal, and only at very short range. Then, in the year 2000, I pulled that GP100 from the safe, and fire a timed qual course, with a resulting cumulative group as good or better than anything I could fire, on a very good day, with a 1911. It is good to know that my ability to operate the GP100’s long-stroke DA trigger is not a highly-perishable skill.
To be clear, this is not about one particular weapon being some kind of talisman, or good luck charm. I have another GP100, just like this one. I have several newer GP100 revolvers, that do not have the grunge-eating grooves, but they would probably function well, through a prolonged gunfight scenario, if I use clean-burning, good-quality ammo.(Modern duty ammo really does burn quite cleanly. It is the cheap practice fodder that leaves unburned powder residue all over the place.) I could substitute a good K-/L-Frame S&W revolver, if it had suitable aftermarket grips/stocks, that fit me well. Other good revolvers, such as Colt, Dan Wesson, Manurhin, Korth, etc, would probably do nicely, if they had grips/stocks that fit. N-Frames are a bit too large, for me hold properly, and be able to reach the trigger.
Much as I love my SP101 revolvers, there is less “work space,” for reloading in a hurry, so, in a scenario that requires that I have only one weapon, the choice will not be an SP101.