Based on the way Stirling speaks of him, I'd say Fangio.
José Froilán González would also explain how Fangio, who was at the time driving for Alfa Romeo, took him to Silverstone on the day before the 1951 GP to teach him all the track's secrets and how to maximise his performance there. It was González's first race under a proper Ferrari contract, and Fangio knew how important it was for him to perform well, even if he also knew that the track was much better suited for the Ferraris than for his Alfa Romeo and that, in all likelihood, he was giving his young friend the information he needed to beat him.
Also, González explained that, when Ascari's car broke down during that race while González was leading, he was expecting to be asked to give his seat to Ascari (as his contract stated), but that Ascari himself told him to stay put and win the race. And win he did, the first GP victory for Ferrari, giving González a place in F1 history books - thanks to the gentlemanly behaviour of both Fangio and Ascari.