I have used Mobil-1 in all of my gasoline fueled vehicles for over thirty-five years and try to change it at 6,000 mile intervals. Most of those vehicles have run over 150,000 miles and all but one were still running strong when I sold or traded them.
I figure that oil is cheap insurance, particularly in a high mileage vehicle that might not be worth repairing if it incurred a major engine failure. I have Wal-Mart Tire & Lube Centers (TLCs) do my oil changes, but I ALWAYS WATCH THEM to insure that they put the proper oil in.
I use Mobil-1 High Mileage 5W-30 during the colder half of the year, November thru April, and 10W-30 during the other, warmer, six months.
If your vehicle is going to be heavily loaded and/or you're going to be driving a lot of steep grades, I would opt to change oil sooner, due to the load on the small engine.