What oil is best?

I wouldn't run straight 30 wt oil, even in LV. You will have easier starting w/ 10W30 or 10W40. You can use 20W50 in LV and might be better if your engine burns significant oil <1000 mi/qt. There is also "high mileage" oil, which is probably just thicker.

Definitely don't use the cheap 30 wt non-detergent oil you see in Dollar stores. The detergent suspends the black carbon so it doesn't wear the metal. The main difference in diesel oils (CJ rating) is more detergent, and many people use that in gas engines.