Bristol Centaurus is pretty good contender and the Napier Sabre is proof of the evolution of wartime development thinking even if towards the end of the war you wernt checking your six as much as your engine instruments.

Wasnt the griffon an earlier design than the merlin? – if so, for the underdog to overtake the merlin makes it a contender? –

Ultimately if the context is ‘wartime’ engines and not just piston engines the merlin has to win doesnt it?

Having said that if the Griffon was earlier, it spawned the Merlin then Superceded it right up to the good ole shackelton. (my facts could be wrong).

My money is on the Griffon – and youve got to thank it for the way it improved the look of the spitfire, without it would we have had the distinctive look of the later mark spitfires – (and less to argue over!)