Physical copies, hands down. I just feel like digital is unreliable in the long run.
PHYSICAL COPY
Pros:
-less likely to corrupt
-can resell someday if I wanted
-doesn't take up space on the SD like a digital game
-can play on a future system (if it is backwards compatible)
-can buy a used copy for less
-can buy at any time, even after Nintendo has stopped selling it in it's store (or the store becomes obsolete) [think long-term like 10 or 20 years from now like what an NES game is today]
Cons: ??? I've never lost a game so that's not a problem for me. I can't think of any cons, lol. They take up shelf space?
Also a con for a digital game would be what if your DS (or other platform) or SD card breaks or stops working? Not sure how digital copies can be recovered, if at all.
A pro for a digital game is the convenience. You don't have to go out to a store to get it, or wait for it in the mail. It's basically instant, download time aside.
Arguably a digital copy IS a physical copy. It is stored on your SD card, though you could store more than one game on there I suppose.