This is way too hard a question. It seems to me a firearm I would not sell, even if it's not worth as much as other things I could sell. It needs some history to go with it to make it favorite. I have favorites in different categories, but not just 1 overall.
Here it is, My Remington model 788, in caliber 7mm08, carbine 18", bought new in 1978 for $158.00 at Gibsons discount store. I learned to reload because of it, I learned how to free float a barrel and glass bed it, I learned how to develop accurate reloads because of it, learned how to install and adjust a Canjar trigger because of it. It showed me the joys of taking something inexpensive, and making it perform like something that is expensive, it helped teach my wife how to hunt. It won every hunting rifle match it ever shot. It harvested game with complete humaneness, it just doesn't miss. I actually feel bad when I take my Model 7 hunting in the same caliber, because it's so much lighter, and will take the 788, just because of Karma sometimes, so it doesn't get jealous, the model 7 will never win a hunting rifle match, unless there is a category for rifles weighing 6.5lbs or less with scope.
I still have the group that it shot and I carried in my wallet next to pictures of family, .469" 5 shots @ 100 with a 6 power scope.
Lets hear yours.