A lot of good oils out there today-------especially the synthetics from a major company. Mobil 1 is a good choice and is available in lots of different viscosities. A 5w-30 would be the most common choice, but some of us run heavier viscosities in our gas MH's because of the duty cycle and the potential for running hotter than normal (climbing a long grade pulling a toad). I've used 15w-50 for a lot of miles and (for the sake of one oil in several vehicles), I'm been using Mobil 1 Turbo Diesel 5w-40 for the last couple of years. It is also rated for gas engine use SM and SL.
Mark
2000 Itasca Suncruiser 35U on a Ford chassis, 80,000 miles
2003 Ford Explorer toad with Ready Brake supplemental brakes,
Ready Brute tow bar, and Demco base plate.