I got hooked on peanut butter during a 6 month stay in the US and have also noticed a lot of variety in the products available here (Denmark). I really dislike most of the products, but have found a discount brand that is now my favorite.

All of them are 99% peanuts, so I also wonder where the variety in taste comes from. My own theory is that it is a combination of the following: 1. How much the peanuts are roasted. 2. How much of the peanut ends up in the product. Some have a strong bitter taste that I suspect is from skins that haven't been properly separated from the peanuts. 3. Emulsifiers. 4. Oils and 5. Sugars.