"Best" is subjective. I do believe Toby is correct.
That said to best is first a gun that fits the shooter, properly choked for the shooter's style of shooting and type of game, 100% quality engraving, good wood, excellent to near prefect metal to metal and to wood fit, checkering done as near prefectly as can be seen, and balanced.
I believe some round actions do qualify. Maybe a box-lock? I do not own any round actions, but still lust for one, and regret the field grade german round action i had but traded away.
I have seen some American guns that might qualify, one 16 LC A2 (I think it was an A2) or premier was so near prefect I still curse myself for not buying it. But the reality is the big London makers set the bar. I do not own any London SLE best, and probably never will, but i do own several Belgian SLE, all made in the 20's that meet the London mark without the name.
I love beautifully executed and technically near prefect guns. Given mechnically sound design and actions in the end a best gun is the one you shoot best
