3DS is good if you like Nintendo's games, the usual Dragon Quest/Monster Hunter game and one or two decent JRPGs, everything else, from library to specs ranges from mediocre to atrocious.
Vita is good if you like a large library of multiplats on the go, great specs+controls and a huge library in general, Sony's first party support was half assed and the only big names on it are either western franchises or niche JP games for a more hardcore audience.
Both systems have a fair share of untranslated games that are really worth it, the Vita has a slighter advantage in terms localizations, but since most games are multiplats you have no reason to bother unless you really want a portable, there are still a few really great JP only exclusives on it though.
The 3DS is much easier to break than the Vita, which requires 3.60 or earlier software and proprietary memory cards, but ironically the Vita is also easier on the actual hacking side, not like the 3DS is hard to hack at all, but still.
If you cannot afford both like any respectable Idort, I'd say buy a Vita since it has much better specs and a much larger library with much better choice and quality overall, but I don't really care about Nintendo's games as much as you could and I got a bit burned by the 3DS' lackluster library coming from the DS, but take this with a grain of salt anyway, the best choice is always getting both.