I always make this recipe with regular creamy peanut butter and it works perfectly for achieving that smooth, fudgy texture. If you like a bit of crunch and texture, I think that crunchy peanut butter would work really well in this recipe too. Use a regular peanut butter like Jif or Skippy for best results - I have found that more natural peanut butters (the ones where the oil is separated out) usually don't work as well in baking, most likely because they tend to be a little bit runnier.