I recently switched this summer to QS (Quaker State) Defy in 10w30, on our 2007 Prius.
Never has it run so quietly or smoothly...other than maybe the one time I used Mobil 5w30.
In years past, when I was a Subaru owner with Boxer engine, I ran QS once or twice on that motor & really was not a fan of it (became noisy after about 2000 miles with fresh OCI).
Does anyone else have experience using QS Defy in a Prius? This was the oil on clearance last winter at Autozone, and I am thinking of buying some in 5w30 for next winter.