Done much better in 1956
I don't know which version is closer to Molnar's original play, but the 1956 "remake" entitled 'The Swan," with Grace Kelly, Louis Jourdan, Alec Guinness & Agnes Moorhead, is truly a spectacular improvement. I did think the 1930 version was good, too -- but it lacked the brilliant interplay between Guinness and Moorhead, and the beautifully written (and performed) final speech by Alec Guinness.
Anyone with an appreciation for superb writing and flawless perfection of performance MUST see the 1956 version.
Older, black & white versions often suffer in comparison with later color remakes -- especially when the costumes, jewelry & sets are this flamboyant -- but this is not the prime difference between these two adaptations of the same play. The writing and spectacular performance -- by a much better cast, of course -- is what sets the later version apart. The last half hour, in particular, are unforgettable, and should be seen especially by any fan of the great Alec Guinness, who is certainly at his best.