If I’m strictly applying your rules of “off the shelf” and “NEW” I’d recommend taking a hard look at the K6s with the only addition being the new Hogue bantam grips. Though the other revolvers on the list are excellent, each of them would require me to do some fine tuning for my preference. The K6s comes “off the shelf” with sight options and a super slick action. For me, the K6s shoots like a larger framed revolver with the Hogue grips.
If you plan on running a “torture test” sized round count of max pressure magnums then the GP100 would get the nod.
If you didn’t mind investing in enhancements, don’t intend on running solely max pressure magnum loads, the S&W K frame might be the top runner with a smooth and tune action job, aftermarket grips and upgraded sights.