Now this is my personal opinion only. Ask a thousand people and you will get a thousand different answers.
One of a very few favorite folders was a Schrade made Buck contract Model 303. BUT, you could not twist or push them hard. Fit and finish were as good as a factory production knife gets.
Later the early models of the riveted scale Camillus contract Buck folders were nice also, I think just because I liked rivets on the scales. If you like a big pocket knife the large 307 model Stockman was always finished nicely.
I would say that Camillus era continued to improve till the end.
Some of my favorite Buck made era folders are the late 80's models, flat ground blades, 425m steel, several scale options. If I could only keep one 301 stockman, it would be my elk scale 301 from the late 80's.
For my recent choice I will say the Rosewood scaled, brass bolstered models. Considering your favorite model the 309, I think I would choose , another elk scale ....300
Late 60's Schrade 303
It's a touch small for me ,1971 model 305, but I just like the big rivets and the way the long pulls are stamped, in these oldest Cami's.
'Likely' about the late 1980's. Model 307, you know you had it in your pocket.
1988 'This is my Corvette.'
2008 309, not flat ground but will get to have the 420hc Bos in elk scale.
PS None of these are in production. Look in the Here and Yon.....