Obviously my three (Orlik) 3/4 OZ briars. But also my 50's Stanwells - most of them are c. an ounce in weight, and the bent ones are an effortless long-lasting clench.
My Savinelli 673s (I have 4) are excellent clinchers. Perfect shape and balance for clenching. In fact the only thing that keeps me from clenching them continuously is how perfect they feel in hand.
Clenching never felt comfortable to me. I have always tried like Brad’s picture, positioned two or thee teeth away from the front teeth. Then I read warrens post about using the molars. That to me felt more comfy. I’ll have to try that for several pipes, see how it goes.