Are you painting to match some existing paint, or is it going to be 100% new paint?
If 100% new, I’d use light. BUT: you can test this. There are even test strips printed for this. 1/2 light, 1/2 dark. You spray over it and then compare to the existing paint to help guide you to the right primer.
Take a sheet and primer it 1/2 and 1/2. Paint over and pick what you like, or hold it against existing paint and see which matches better.