NP or rare prisms?

Probably NP is best, until that's maxed out.

If you are absolutely sure you won't be using them all that often and won't regret burning them, there's no reason to keep them around. Otherwise, don't, you never know whether you'll get them again.

Anne & Mary are good nukes, Astolfo I think you can burn him without regrets.

You can put the extra copy in second archive while you decide.

Anne and Mary were my first gold rider and I would have np2 them in a heartbeat. But now I have kintoki rider and I don't use them much anymore, so if I get another copy... Well depends on what is in the rare shop. Though I already have 2 copies of Fion to gleefully burn...