I believe it's really up to you to decide what to get, but I'm still going to give you some advice.
If you get ACNL Cards, you can also get the Calendar as well with your leftover coins. If you're into exclusivity and want to proudly show these prizes to your friends, this is the way to go.
Kid Icarus: Uprising is quite a great game packed with a lot of content. If you can't afford the game at the price of $34,99, then spending 700 coins on it is a great idea too. You can then use the remaining 300 coins for another downloadable game. A perfect way to spend all of those remaining coins would be NES Remix, Dr. Luigi, Dillon's Rolling Western: The Last Ranger, Fluidity: Spin Cycle, HarmoKnight or even getting two Game Boy games (best combo would be Donkey Kong and Super Mario Land 2). Don't ever bother with Grill-Off with Ultra Hand and the greeting cards!