I summoned a Celica, who should I give Distant Defence to?

Well, who do you have who could use it?

I'm thinking about putting it on my dancer (lightning breath Ninian) with CD seal since she wont ne initiating much, just taking hits

Well, basically any mage tank appreciates distant defense, if it has’t got another important a skil.

If you have a (regular) Leo, his Effect-refined Brynhildr combos really well with Distant Defense in the A-slot, as it allows him to run an omni-breaker set against all Ranged units with his innate Quick Riposte.

Aside from him, you could put it on a DC unit or a different Ranged unit with high Def and/or high Res.