Blueberry provides acid color and some aromatics.
Lemon provides aromatics and a lot of acid note. It does not dominate so I use it to bring up flavors lost in fermentation.
Passion fruit provides nice aromatics.
crab apple can provide tannin and aromatics.
I like aromatic apples.
Cranberry provides weak aromatics lots of acid and long tannic like notes.
My basic look is to ask “ what is missing and look for a source.