Chevron vs. Valvoline oil

I once read an article about an extensive study of the use of various brands of oil (they used the rating recommended by the manufacturer, but some oils were inexpensive off-brands) in a very large new taxicab fleet, with several oil-change regimens (identical engines, all maintained by the same in-house shop, one oil brand and oil change frequency used in a given vehicle). Engines were torn down and measured for bearing surface wear after considerable mileage (can't recall the exact mileage, but I think it was well beyond 50k miles). The net of the findings were that the wear differences between oil brands were not discernable; the big factor in wear was the oil change interval (as might be expected), and I think they said if the oil & filter were changed at least every 4k miles, the wear was minimized. One caveat, I suppose, is that taxis are running night & day, rather than being taken for short trips and then unused for long periods.

My advice is to change the oil & filter frequently (I use 3k mile intervals) and don't worry too much about the brand.