I’m not sure how or why grape became the default. For the longest time, I thought I didn’t like PB&J. But ever since trying it with strawberry instead, I understood the appeal. It’s so much better, and now I find it weird that the combination isn’t more common.
Coarse ground peanut butter but not crunchy, with a little salt and honey, plus blackberry or boysenberry preserves is the way. That or a fluffernutter.