[GloriousKoji]

Jif uses molasses where as most peanut butters just have plain sugar. I suspect this is primary difference in flavor.

The creamy solid frosting like texture of peanut butters like Skippy and Jif comes from the high content of saturated fats, which are more solid and shelf stable at room temperature. Traditionally they use hydrogenated vegetable oils to achieve this. The newer "natural" versions just use palm oil instead, which is naturally higher in saturated fats.

I also wouldn't be surprised if the type of peanuts used are unique to each company. Many of theses mega corporations breed their own specific cultivar of produce for their own use. Examples of this is (Nestle) Libby's pumpkin and Lays potatoes.