WOW! There's a question to start a battle...I am sure you're going to get more answers than you can sort through in a month of Sundays.
So my answer is going to be....."It depends".
Now, I don't like to tell people what to do with their own vehicles, so I'm just gonna tell you what I do, ok?
Get ready...this is gonna be quite a bit of info.
I got a 1992 S10 with a little over 200k in the clock. I run Castrol GTX in it, 4 quarts+1 quart Lucas, gets driven MAYBE 15-20 miles every month or two, basically just to keep everything lubed, and the battery charged. I change it every 3 months.....or whenever I remember! *LOL*
1990 crown vic that I inherited from my (now deceased) grandmother. It's my DD, with nearly 100K on it. use Pennzoil 10w40 in it, 90 mile round trip every day, half country road, half highway. Change every 3,000 religiously. Currently in search of an engine from a '95-'96 V8 explorer for this puppy, if I don't sell/trade 'er first.
Bought the wife an '06 Fusion. It now has 70k on it, run Pennzoil 5w20 in it,
(5w20 is what Ford says use) 90 mile round trip, strictly highway every day, change it about every 5,000 (Again, as per Ford) sometimes as late as 6,000.
So ya see, it depends on mileage, useage of the vehicle, how much it's driven, how far it's driven every day, manufacturers recommendation, and of course, personal preference.
Joe.