The short answer, for me, is that a 6" L-frame, with just the right grips/ stocks in place, loaded with .357 Magnum premium 125-grain defensive ammo, would be a fine weapon, with quite tolerable, controllable recoil, irrelevant flash, and an exhilarating blast. Even the lighter Model 19 or 66 would still be fine. Indeed, my latest duty sixguns, as late as 1997, were a 19 and 66. (I believe in spare weapons.) I carried larger-framee sixguns before the 19 and 66, including a GP100 I used to fire a decisive defensive shot. I don't know if my incident figured into anyone's stats on stopping power, but it sure made an impression on me. (It was not a surprise; I had already read of the stats and studies, but local reputation was also important. The 125-grain .357 was already King of the Street at that time.)
Keep in mind that the flash and blast are worse on the bad guy's end! A flash-bang that punches a hole; what's not to like, from a defender's viewpoint? That being said, I may choose something else for a dedicated indoor weapon to be used in tight spaces; this is where I like .45 handguns.
Recoil is complicated; much depends on the fit of the weapon. The original, pre-Hogue
GP100 factory grip is a somewhat better equation for my hands than any K or L grip I have yet found. This is more for comfort during sustained fire; I would have no problems using an S&W K or L for the few shots involved in a defensive scenario, though my Model 19 is kept loaded with 145-grain Silvertips these days. (125s are still my load of choice in the heavier GP100, which is the size-weight equivalent of the S&W L that is the topic at hand.)
Lastly, be wary of the "truck gun" concept, if it means leaving the weapon inside the vehicle. Burglaries of vehicles are the LEADING reportable crime in my area, which is typical of all urbanized areas of the USA. The harvest of firearms taken from vehicles is huge around here during such times as the rodeo, when country folks leave their guns in their trucks at hotels. Hidden is not enough, and NO place is safe. Please, do more than just hide the guns, and keep in mind that the large screwdrivers and small bolt cutters typically carried by car burglars can make short work of cheap security measures. I am not parroting anything; I wear a big-city PD badge. I not only respond to the scenes, but see the cautionary notices on the computer screen, of weapons stolen from vehicles, or along with the vehicles, from throughout the area. Sorry for drifting from the subject, but I feel strongly about this.