So Many
Hard to pick just one. There are so many.
My favorite "rare" knife is a Holley Wharncliffe Whittler. I owned one when I was young. Gift from grandparents. Lost it in England. I would be happy with a Case Classic version of that knife if I could find one, and happier still if it was in original CV steel.
Barlow? I have some. One of them pretty good. Somehow never really been able to warm to the pattern like I do some others.
Sod buster. Yeah, that's a knife for which I have a real fondness. Simple, robust, versatile, easy to carry and maintain. A true classic. Sodbusters rock.
Stockman. Another classic. Also versatile, easy to carry and maintain. Touch of class, suitable for "gentry" carry. Love my Case John Deere in green bone.
Folding hunter. I really like the pattern. Mine is a little large for EDC. I prefer the pattern, marginally, over the Buck 110. Ironically, the Buck 110 gets carried more often.
Muskrat. I have exactly one of these. Now, mine has a "toothpick clip" blade and a full-length spey blade. That makes it essentially the equivalent of the trapper, but with the blades mounted at opposite ends, rather than side-by-side, so the Muskrat is thinner (one spring as opposed to two). I've become quite fond of my Buck Muskrat. Carry it a lot.
Scout knife. How can you not love a scout knife? That's the pattern my dad gave to me on my twelfth birthday. I still have it. I still use it now and then.
I have an assortment of classic fixed blades (Buck 119, 102, etc.) but I don't really get an opportunity to use them much. I suppose if I lived a bigger part of my life outdoors with more camping (okay, any camping) then one of those would be up for consideration. But not at this time.
Favorite?
Well, of the American classics, I think I'd have to say stockman, particularly the Case and Schrade Uncle Henry patterns (both have the slender toothpick-style main blade). Based on my tendency to favor the stockman when choosing daily carry pieces, I'd say that's about right.