Depends what you're looking for.
If you travel at all, iPad's fantastic. It's not as bulky as a laptop or even a netbook, it does games, it has a far better browser, you can also stick music and videos on it. Its virtual keyboard is even big and well laid out enough that you can touch type on it. I have to do quite a few long train journeys each year, the iPad's a godsend for them.
While the 3DS has promise, I regret getting one so soon. It's still yet to develop a decent game library. Over time, it'll get better games AND it'll be cheaper.
My final answer would be either the iPad or neither, for now, depending on what you want - if you travel or have other periods of time of doing nothing, the iPad will be good. If you're mostly active, there's less need for it. Leave the 3DS for perhaps half a year. That way you can also compare it to the PS Vita in its state at that time.