I bought my bronco in 1998 with 46K on it. I immediately started using Castrol Syntec 5w50. That oil is perfect for my climate. It's just a WIDE range of protection for an oil... nice. I use nothing but Wix filters, as I've seen the inside of others and was not impressed. It costs me $18 for a 5qt jug of oil, and $3.99-$4.39 for the extra quart. I usually buy 2 filters at a time, which run me just under $10.
I was using Castrol GTX 20w50 in my buick regal before i got rid of it... It had 280K on it, and needed the thicker oil to keep the thing runnin' smooth. I live in the upstate NY area, so we get temps from 0's to 90's.
1994 Ford Bronco XLT - 302cid, E4OD, 32x11.5x15 Dunlop Rover RV, Rancho RS5000