If you don't care about 3D then the n2DS. But if you've never tried 3D on a n3DS you may want to find a way to try out or borrow a n3DS to test on. It works way better than on the o3DS, thanks to what they call "super stable 3D", essentially it tracks your face so 3D works no matter how you hold the console.
I believe it would change the opinions of a lot of people in regards to 3D on 3DS if they tried it out. I can see why people didn't like it on o3DS, it was a huge annoyance and I could never really play in a relaxed position, but I still persisted because of the additional immersion it created.
With the n3DS I see no reason for anyone to play with 3D off, unless they're one of those people who get headaches/nausea from 3D (even that might not happen with the n3DS since you don't need glasses) or the game they're playing runs poorly with 3D on.