Zimm: As you're finding out, asking Forum members for their suggestions on which S&W revolver to own opens a huge can of worms. There are a few common threads, but probably still a hundred different options being tossed out! But since you asked, I'll play along...
Although I am primarily a vintage N-frame guy, I do have a few K- and L-frames in my modest collection. I think that your Mom has great taste because she "borrowed" one of the "best of the best" revolvers from you- that Model 19-4. I think that the 19-3s and 19-4s are some of the nicest mid-weight .357s, and smoothest shooters, that S&W ever produced. I can't speak for the Model 66s. I also like the Model 686s, especially the 7-shot Plus models. For the time being, if I were you, I would be looking at vintage P&R revolvers instead of the brand spankin' new unproven offerings from S&W. The vintage revolvers are proven shooters, and often the price is the same or better than the current production models. Blued, nickel, or stainless is up to you depending upon your range use and personal preference. Unless you're having an epiphany like jakerudy, or you just won the lottery, I wouldn't consider buying a Korth, Manurhin, or SPOHR revolver. Beautiful and wonderfully made, yes...but I have better uses for my money. Good luck with your decision, and please let us know what happens.