In terms of de-duping, either area of import will de-dupe by default. If these are new leads from an event or something similar, my recommendation is to import them into Marketing Activities under the associated program. If these are leads that are being updated with field values as part of an import, then I would keep them in Lead Database if they are not part of any specific program.
Yes, Safia. As Devraj mentioned either way will dedupe - just be sure to include email addresses on import as that's how Marketo deduplicates leads.
I'd recommend using static lists but underneath the program level. This way you can better reference and report off these lists but it also allows better organization and reminds you to have flows set to ensure on import xyz happens (acquisition, lead source, lead source detail, etc.).
And just to be clear, leads that are imported directly into a program in Marketing Activities, are part of the master database. Those that are imported directly to a program are just more easily referenceable and easier to assign program membership. But either place adds them to the master DB, where normal deduplication rules apply.