Lets Say it's a gun or guns that have been reliable, that serves its intended purpose well, and that hasn't been repaired or modified since you got it
Following that criteria I can't single out one particular gun. Discounting used guns because you stated out of the box I can think of seven right now that were trouble free from the beginning, and still are. All from different manufacturers. Bretta, Browning, Glock, Hi-Point, Kahr, Ruger, and Springfield Armory.
All have given adequate accuracy for their intended purpose. Some exceptional accuracy. From target shooting to CCW, to hunting, all have met their intended purpise.
I would say the most surprising was the Hi-Point. A 9MM bought to just see if they could possibly be as bad as the haters say. Not only is it 100% reliable, it is one of the most accurate 9MM handguns I have. Easy, and fun to shoot it fits the role of range blaster perfictly.