I like to buy a wheel which matches the others on the truck, then buy 5 tires and do the 5 tire rotation. I'll usually keep the factory spare as a spare spare then for long trips. Having the 5 matching wheels makes the 5 tires last 20% longer since each one is not being used 1/5th of the time. I usually replace them after a few years before they reach the maximum mileage that way so that way I'm not driving on worn out tires right before buying new ones.
I keep the old tires and give to my father for farm equipment.