I voted K-Frame but its not my favorite. All of them are except the J-Frame .357s [which I consider a bad idea for most shooters].
I have first of all always loved the "looks" of any N/L/K frame S&W .357.
The N-Frames, with their tapered barrels and full array of metal contours are just plain sexy. Full house .357 loads are a pussycat.
But wait....the L-frame is just as sexy, especially in nickel. And all of them are so beautifully balanced. Especially the 4 inch round butt versions. The fixed sight versions have got to be exceptional as to handling as well although I have never handled one.
However....the K-Frame is light, easy to carry, handles well, will shoot the "occasional" .357 load which, probably most shooters also only occasionally shoot fullhouse .357 loads. My most favorite .357 in balance and handling is a M13-2 blued 3 inch with Pachmyers.
If I were an LEO I would carry that with my R-P 140 grain hollowpoint loads anywhere and all day. If allowed of course.