Your original has the proposition functionally stranded given that the most serves only as an amplification. Paint me an old fuddy-duddy, but preposition stranding is something I try to avoid. It was the tail on which he most prided himself. The tail was his singular pride. Above all else, the tail was his pride. All else paled in comparison to his tail.
Ah, I knew it sounded wrong in some way. Perhaps I could add it on to the previous sentence, avoiding the problem - That said, I really like your third suggestion - thank you!
Cool, glad to be of service, though... just to be clear, the version wherein you add the other sentence still has the same stranded preposition. Again, I realize it's the old-fashioned grammarian in me that sees that proposition as out of place. I won't say I make a religion of it, but where possible - without too much in the way of verbal gymnastics - I try to structure things the way you did in the second part of your original post. Here the proposition is placed in what I find to be the more natural order, hence the term pre + position.
Thank you for your help - I've changed the sentence to one of your suggestions. Prepositions are always the thing I find most difficult
@severine , dare I ask who you are writing for? Wondering because you are choosing to write in such a formal manner, for example saying that your dog is “in possession” of four paws, rather than just saying: Being a big animal, Freeway had four strong paws. His glossy silver coat was magnificent. But it was his tail, cleanest in all the world, he was sure, that made him most proud. Simple language and simple sentences are far more readable (I think) unless you are trying to establish some “voice” with a more stilted or formal speech. I agree with @Wreybies about the awkwardness of the floating preposition, but (to me) your choice of language was awkward as well. Just saying...but I like to keep writing simple.
