The Philadelphia Story. Just, as good as it gets, with three of my all-time favourite actors - Cary Grant, Katherine Hepburn and James Stewart - wringing every last drop out of one of the greatest screenplays ever written. Just flawless. Also featuring one of the best ever performances by a child actor, in the form of one Virginia Weidler, who among other things gives a cracking performance of Lydia, the Tattooed Lady. I've seen it before - more than once - and I will most definitely see it again.
One thing I didn't know till I looked it up on IMDb is "Hepburn wanted
Clark Gable to play Dexter Haven and
Spencer Tracy to play Mike Connor, but both had other commitments. Grant agreed to play the part on condition that he be given top billing and that his salary would be $137,000, which he donated to the
British War Relief Society."
IMDb somehow only arrives at 8.1. I can't see any excuse for anything under 10.