First, mins you, none of the oils below of for only 1 vehicle. I maintain 4 vehicles at my home. My 09 MS3 GT, wifes 01 GMC Jimmy, my daughter's 10 Cobalt and future son in laws 10 Focus S. This along with our 8-5pm nurse and sometimes my father in laws truck and TDI. Also my best friends 00 Mustang GT and an 06 Blazer (yes, I do all of these believe it or not!).
Anyhow, I've used, tested and drive... Mobil 1 10w30 HM, Mobil 1 15w50 Racing, Mobil 1 AFE 0w30, Mobil 1 5w20, Valvoline SynPower 5/10w30, Pennzoil Platinum 5/10w30, Pennzoil Ultra 5w30, Rotella T6 5w40, Red Line 10w40, Castrol GTX 5w30, GC Syntec 0w30, Royal Purple 0w40, Castrol Edge 5/10w30.
Of all of these, hands down, the smoothest/quietest oil was Castrol Edge 10w30! There is absolutely NO question. I am emphatic on purpose.
...I still have these in my stash to try yet...
Pennzoil Ultra 5w40 Euro (thanks Debbie!), Havoline DS 10w30, Pennzoil YB 5w30 & 10w40, Mobil 1 10w40 HM, Mobil 1 0w20 AFE, Mobil Clean 5k 5w30, Quaker State 5/10w30 Ultimate Durability.
...I plan on buying these to try too...
Red Line 0/5w30/40, Mobil 1 0w40 Euro, Mobil 1 5w30 ESP, Mobil 1 5w30 HM, Amsoil 5w30 European Formula, Royal Purple XPR 5w30 & 10w40, Motul 300v 5w40, Valvoline MaxLife Full Synthetic 10w30 and regular Shell 10w30.
But again, there is absolutely no question in my mind, at all, the quietest and smoothest so far was the Castrol Edge 10w30.