Does it have to be a new gun? I own stacks and stacks of Rugers… if I was pushed into a corner and had to pick "my favorite," it would be very hard to pick a New Model over an Old one. My absolute favorite would probably be a Clements custom that I bought on the Ruger forums. 4 5/8ths barrel, OM, all the special features you would expect, .44 Special. Even has the Clements OM Bisley hammer on it. All case hardened. Really beautiful gun and just great in the hand.
Second favorite would probably be a .44 Special I had built for me. OM .357 conversion, 5.1" barrel, two tone, locking #5 Belt Mountain cylinder pin. Handy gun, easy to carry and shoots great.
If we HAVE to deal with NM's and factory guns… I did really like the 50th Anniversary models. My .357 50th is probably the best NM I ever bought factory new. Just seems to magically hit right where I look. Great feel, size… everything. Except it isn't an OM!
Finally, if we are going to leave single actions and move to double, I have two favorites. OK, plus an extra comment! My favorite of my "old and discontinued DA Rugers" is a 5.5" stainless Redhawk in .41 Magnum. Once I put some of the fancy European grips on it, it's about perfect. The best "new Ruger" I've bought in the DA area is my seriously fun Ruger Alaskan in .480 Ruger. Easy to reload, just a whale of a lot of fun to shoot. Large enough to be impressive without being so crazy large that it becomes impractical. Everybody who gets the full tour of my gun collection asks to shoot it. And then they smile. Really big. And ask for more ammo to do it again!
I do love original Security Sixes. And the Ruger DA that I own with the most rounds downrange is probably my 9.5" Ruger Super Redhawk in .44 Magnum. I used to shoot 50-100 rounds through that gun every time I went to the range. Put a stainless Leupold 2x scope on it. The weight of the gun plus the scope calmed .44 Mag down and made it easy to shoot. Even with super hot reloads. I've made a lot of crazy long range shots with that gun _off a bench_ and it will really explode a 2 liter soda bottle at long range. Load a Sierra 180 grain JHC bullet with an absolute max charge of WW296 and it makes you laugh when the bottles explode.
Gregg