The Awful Truth
Just a really, really solid slapstick. Cary Grant is incredible (reading on Wikipedia this was the impetus for his launch into superstardom, which is totally earned); Irene Dunne, who is not my favorite, puts up a superlative back half (her scene as "Lola" is perhaps the best in the entire film.) The movie feels loose and improv-y in a way that few movies of its era do; there are a few bits that age it (my mind is drawn to the very cute and very advanced-for-its-time special effect with the cuckoo clock) but you could do a shot-for-shot remake of this and it'd be well-received.