Getting the digital is just so tempting! The reason I bought a 3DS XL in the first place was because of New Leaf, and I love the idea of always having the game on my 3DS whether I have the cartridge in it or not.
But I'm just so used to having cartridges, and I don't trust the digital version. There are many things that could go wrong with it. It would make me 10 times more scared my 3DS will break and I'll lose my game data. And I heard that it's a daunting task to transfer data to a new SD card if you ever wanted to update to a larger GB (mine is the 4GB). I just trust cartridges more.
And let's be honest, my 3DS will almost ALWAYS have the NL cartridge in there anyway, so it doesn't really matter.
Sure, it's nice to think of how if you get the digital, you'll be able to get the game ASAP at midnight, whereas you have to wait till morning to get the physical, but if you're a non-time traveler like myself, there most likely wouldn't be much for you to do at when you get the game at midnight, because after the tutorial or whatever, everyone would be sleeping and the stores would be closed.
Plus, I really love the excitement of rushing to the store first thing in the morning, buying the game, looking through the manual and waiting impatiently in the car to get home and play it.