Mobil 1, been running it since it's second oil change. I used to change oil every 3000 miles. Now that I use it mainly offroad I change it 3 or 4 times a year regardless of the mileage. Filter is Fram.
I also change my manual tranny fluid about 3 times a year and use Mobil 1 ATF.
Diff fluid gets changed twice a year.
A lot of oil changes sure, but I figure it's cheap insurance.
My manual tranny fluid used to come out solid black when I used the factory reccomended intervals or slightly less than reccomended mileage. I just changed it yesterday in fact, in preperation for the Moab run and it was still nice and red.
I'm a big fan of synthetic oils no matter what the brand, I just happened to start with Mobil 1.