You will get 8,000 different answers to this one, about as many as what type of wax to use
Above 0 deg use 10W-30. 5W if it's colder. Use a synthetic if your wallet does not mind...self change it at 5,000 drain intervals it will save money in the long run. Use a NAPA filter!
Personally I've used Mobil 1 syn after 15,000 miles in 9 vehicles now for literally hundreds of thousands of miles. I usually change it myself, Sam's club has pretty good prices on it. Who knows if it provided anything over regular, sent off a sample one time @ 109,000 miles on my 4.0L YJ and they said everything was perfect and I could stretch the drain interval.
My favorite quote from a vehicle owners manual "use of any fluid or additive not suggested in this manual will only increase your total cost of ownership"
If you really want to see some oil opinion wars, check out some diesel forums...those guys go crazy over oil