I buy whatever 5w-30 motor oil is on sale at the local Advance Auto. Usually their house brand (packaged for them by Ashland Oil). I change every 5K miles, and will change it at about 3K miles if I am do any signficant towing. I use Purolator PureOne filters. My 2001 ST has 66K miles.
Im my opinion, for natural oils, there is no reliable way to separate the advertising hype from the reality, in terms of performance.
A few years ago, one of the Trailer Boats Magazine tested various oils in some of the new 4 stroke outboard motors that were just then hitting the market. Marine motors are often worked very hard (higher average RPMs, big loads, inefficient transfer of power), and subject to a lot of corrosion issues, so it was a good torture test for the oils.
Pennzoil's basic automotive stuff outperformed all of the twice-as-expensive OEM branded (Yamaha, Mercury, etc.) oils, despite the motor manufacturer's recommendation to use their oils in their motors. If I recall, Valvoline didn't fair well. The only oil that did better was Mobil 1, which cost several times as much.
No question that synthetics are superior. They really shine when you are doing things that would normally stress/break down natural oils (such as working the engine really hard for extended periods). It's just a question fo whether you want to spend the extra for the synthetic. If you don't take advantage of the longer change interval, it's a bit of a waste.
As to where you get serviced, my opinion is: Ask your neighbors where they go and find out who is trusted. Even a quick change oil place is fine (regardless of brand) IF they have a reptuation for doing good work.
