On the assumption that “favorite” means a shotgun that I own, as opposed to one that I’d like to own; I’d say the SKB 100 side by side. It was a very nice bird Gun when I bought it. Now it’s cut down and slicked up for cowboy shooting.
I really liked my Remington 1100 but just sold it this weekend. Reason being that I just bought a Remington 11-87 left hand premier. I'm not a lefty but have poor vision in my right eye which has me shooting left handed. I think it will be my favorite now.
I have a couple of shotguns that I really like...Benelli Super Black Eagle, Beretta White Wing O/U but my favorite is my Remington 1100 that my mom bought my dad for Christmas from the Sears catalog in 1968. It had a fixed improved cylinder barrel. The thing still looks great and shoots like it did the day it was bought. I still shoot it once or twice a year dove hunting. My father passed away six years ago. Every time I shoot it it takes me back to when I was 9 or 10 years old out with my dad in the woods or in a field. I wouldn’t take a million dollars for it.