I'm assuming you mean Mobil Super synthetic vs. Mobil 1.
MSS is their cheapest synthetic, and "outperforms conventional oils", and M1 is their premium product.
MSS is guaranteed for 7500 miles vs. 10,000 miles for Mobil 1.
They also use entirely different additive packs.
They're both good oils but MSS is made to the price point of cheaper synthetics, and Mobil 1 is their flagship oil.
2006 Buick Lacrosse 3.8 V6 150,000 mi
2015 Chevy Silverado LT Z71 5.3 V8 30,000 mi
2010 Toyota Sienna 3.5 V6 150,000 mi