Wow! What a tough question. Your favorite can be functional -assuming it is a factory purchase, one which happened to be the right fit and hit most often, what you shot at.
Or, it is one that you had specifically fitted, that turned out to be what you expected and it hit most of what you shot at.
It can be a favorite of your Dad's or a close relative that had an impact on your life, that fits and hit most of what you shot at.
It can be none of the above, but the bottom line is it hit most of what you shot at.
Given all those situations,
My Model 12, 16 GA pump is a favorite. My second shotgun because the first was a Sears Bolt action that malfunctioned and was replaced by the model 12 that hit most of what I shot at.
My AYA Spanish 20GA double that I happened to meet at Sears in 1971 for $50 that took the first 13 rabbits and pheasants I shot at. (When I saw it was an AYA I went back and they were all gone - or pulled).
My Ruger Red Label 12 GA O/U that does as well as those shooting Sporting Clays or Trap compared to any model with a multiplier of the cost.
My Win Model 12 is 12GA pump that has a 30" barrel as thick as a Cocoa Cola Bottle that belonged to an old hawk hunter when that was legal in PA with which I harvested a single Snow Goose traveling alone at 60 yards in the Eastern Shore 40 years ago.
My Savage Fox Model B double in 12 GA that my aunt sold to me for ten bucks when my uncle died took more rabbits than I remember when I was just starting to seriously hunt small game with my Beagle back in 1968.
So, it's not just about the shotgun. But the background that supports your desire to do what it is expected to do.
The "bads?" A 12-GA Weatherby Athena- an absolutely magnificent looking O/U that I couldn't hit my car with it; a 12_GA double S/S - fabulous looking, wooden stock right down to the butt plate. Made in Spain- cost me $1200 - light-weight - but I can't hit anything with it because it doesn't fit.
I hunted with my wife's brother-in-law who would typically buy his license the same morning we were to hunt in PA's first day of small game after we filled up with more beer the night before than I can possibly handle these days. He used an old break-open single shot 12 GA of an unknown manufacturer successfully until he ran out of shells and I gave him some Russian-made shotshells that paused his confidence when he found himself surrounded by the cloud smoke created by the black powder used to make these devils (known to me, of course). He missed the next several shots as a result. No fault of the shotgun.
So it all depends on many factors, many of which are beyond our control on a comparative basis. But most important seems to be similar to what OJ's attorneys said at his trial, "If it fits......"