IMHO, these four things in exactly this order: 1. Engine Lubrication (Does it meet the OEM spec?) 2. Protection (I want my engines to last!) 3. Cleaning/additive packages (Can be a real+) 4. Cost/benefit ratio (Anybody can change every 3K & pay $10/quart: but, do you really need to?) So, with no problems as to whether a possible Warranty Claim is going to be compromised by wrong grade or wrong interval... My answer (in a decidedly mild climate) appears to be Penzoil 15W-40 LongLife and OEM filters (or better) for year-round use. Opinions?