50:1 is approx 2% Oil, 24:1 would be 4% oil. So depending how one looks at it, either could be called Richer. A 24:1 mix would be Richer in Oil(double), but 50:1 would actually be a bit Richer in Gasoline, 98% vs. 96%
If the engine has any Friction Bearings(Bushing), then 24:1 is the safer Option