I switched to QSUD from M1 after looking at the PQIA test results for 5W30, and then switched right back after reading about the potential connection between LSPI in DIT engines and the calcium content of the motor oil used. QSUD 5W30 had moderate calcium levels according to the PQIA, while M1 is low calcium. My car was actually recalled due to LSPI concerns and I passed the leakdown tests with flying colors...no idea if my choice of oil had anything to do with that, of course!
I think that both are great oils for general use and QSUD is a little cheaper at WalMart, but M1 5W30 had a somewhat higher TBN and might be better for longer drain intervals. I am basing this on 3 year old test results, so formulations may have changes substantially...