For me, it is the Buck 112. I think it has the most beautiful lines of any knife. But it's too fat for front pocket carry and find the Buck 500 much easier to carry on the rare occasions I pocket carry a knife. Usually, I carry a larger traditional in my right rear pocket and I just find a larger Buck 110 (and many other knives) more useful.
<Aside on the Opinel>
IMO, the Opinel is a large traditional and the carry issues are similar. Other include the Buck 110, Case Large Sodbuster and several of the larger GECs.
I think there are 3 reasonable ways to carry a large clipless traditional:
1) in a belt holster
2) in a jacket pocket
3) in a rear pocket.
I prefer the latter and sew a vertical seam in my right rear pocket to hold the knife up, right next to the outer seam. I can carry a brass Buck 110 there. It's comfortable, secure, easy to access and most of all, its discrete and doesn't advertise that I have a knife on me.
In terms of one hand opening, Opinels can be opened and closed one handed but comparing them to a modern folder is like comparing a 3-speed Columbus mounted standard transmission to a modern paddle shift. More to the point, if you want to one hand open and close an Opinel, you need to a) learn a new, non-intuitive technique and b) practice it till becomes second nature.
I prefer to drive stick shift cars but got an automatic when it was time to teach my kids how to drive. Opinels are like that.