Damage

Doesn't matter NPs don't get the first card bonuses. Unless that NP overcharge effect grants attack bonuses or specific card bonus then it's best to do NPBB. Cu Alter and Cleo's for example

To maximize dmg, you should use the NP as the first card since it’s not affected by card order while the other cards do more dmg the later they’re used.

The regular buster cards will have more damage due to the first card bonus effect that the np can't have, so NP B B should have a little more damage, especially if the NP gives you defense down or attack up.

Also note the effects on some NP's like Cleopatra and Bedivere will make this even more so.