Annually, my Wife and I each put an average of 15,000+/- mile on our daily drivers and change the oil on the same 6,000+/- mile interval that I rotate the tires. I could probably extend the oil change intervals, but I'm old, rather set in my ways, and don't mind spending a little more money if it buys peace of mind.
I put a lot fewer miles on my occasional use Explorer Sport Trac, Nissan Frontier, and Jeep Grand Cherokee and change the oil at either 6,000+/- miles or annually if they don't reach 6,000+/- miles since the last oil change.
I use Mobil 1 in whatever viscosity and style the manufacturer recommends.
