The favorite gun of mine, of all-time, is the Remington 121 pump that my Dad bought new in the early 1950s. (same model as the one Old Turtle post a pic of above)
Light, well-balanced, super-smooth action & EXTREMELY accurate with just open sights.
Although I never owned it, I used it all thru my teens & into my early 20s. It accounted for too many squirrels & bunnies to remember.
I tried mightily to get Dad to sell it to me, but he never would.
I finally had it re-blued & stained for him back in the mid-80s, as a Christmas gift.
Once I did, neither of us ever used it again.
A few years later, my folk's house got broke into, & the gun was one of the items stolen. Unfortunately, it was never recovered.
..........
As for guns I've actually owned...
Probably the only gun I can call my favorite, would be the 1st Marlin Model 60 that I owned, back in the mid-80s.
Like Dad's Remington, that Marlin accounted for too many critters to count.
During the colder months, for several years, that rifle was always in the back window, even if I wasn't hunting at the time.
It was almost as good to me as that old Remington.
When my 1st wife & I split, in '91, money got tight, & the Marlin was one of the casualties.