Much faster than the original 3DS and a few new features (which I imagine can be installed on previous versions) I'd definitely say the N3DS is the right choice. Not expensive, up to date and no errors as yet. Online seems much more reliable already; trades and battles on my old 3/DS for Pokemon would drop out after 5–10 minutes but using the same connection is much more stable on the N3DS.
Note: QR code hacks won't work so if you're looking to use hacks you'll need a Power Save/Action Replay device.