I own both. Got the 3DS for launch since my DSi was broken at that time. I don't regret it, as this was what introduced me to the best video game series in the world, Fire Emblem (thanks, Ambassador Programme!). I now on a 2 3DS XL and my launch 3DS was sold in favour of a DS lite that I use to play import DS games that came out after the DSi did (e.g. Fire Emblem: Shin Monshō no Nazo ~Hikari to Kage no Eiyū~). It is m most used console at this time, and I love it to death.
I got my PS Vita just this September (or October? I forgot to be honest), and had quite some pleasant experiences with it. It will also always be remembered for introducing me to Persona 4, which is one of the best games I have ever played. However, my 3DS still gets more use, as I not only own more games for it than for the Vita, but also own the more interesting games on 3DS (in my opinion). If there's a multiplatform release between PS Vita and 3DS (which is rare enough), I'll usually go for the 3DS version (e.g. Virtue's Last Reward). Should there be a game that gets only an American/Japanese release, I'd get it for my Vita since 3DS is region locked.

What about if you had both at one point but sold one (3DS) because it was so small but will be getting a 3DXL in the near future?

Where is the option for the 3ds owning me? I mean seriously, the game has an insane amount of software that is really great for this early in it's life.

Well I don't own one and I currenly have 1 game for it but I know Ninty will never let me down with thier handhelds.

So for my first impression. It turns on faster and has a colorful UI presentation but its not dynamic enough, I guess I got used to smartphone type interfaces too much and the online shop feels lacking, I saw more games online for Vita PSN. I hate the 3D, it hurts my eyes. I'm never going to use that. Backwards compatibility is a plus.

Right now I have Project X Zone on it with plans to get Bravely Default next year. Overall 7/10 for the 3DS.

I have both. I bought 3ds March of last year and Vita 3 months later. I usually dont buy systems close to lauch but i foolishly thought the Vita would be backward compatible with the PSN store at least and i didnt feel like getting another PSP.

HW wise Vita blows 3ds out of the water. Its not even a contest.

As a media machine Vita puts 3ds to shame in just about every facet. 3ds JUST got youtube last week. Vita added a panaromic camera so that kind of elevates it above the 3ds one. The wifi is much better. Netflix looks better. vita has Skype, I tune radio, its just a cool piece of tech. But damn is it expensive. The only thing thats on 3ds that really wowed me is streetpass, i love that damn thing. Thats not to say i dont enjoy my 3ds i just use my vita more as it has more stuff and i have more games.

the games, subjective. But i bought more games for Vita than 3ds, hell for the first couple of months I only had MK7. Just got Tearaway and it is great. Their both good systems i just dont know why i prefer the vita library to 3ds. Maybe i dotn care about Pokemon enough.

I have a 3ds and a 3ds XL Red Pokemon edition... I used to own a Vita and a Original Blue 3ds but my sister wanted a 3ds and my Vita was not being used for 6 months so I sold the vita and got myself a 3ds XL Red Pokemon Edition and gave her my launch edition 3ds... Obviously I transferred all my digital games but I did buy her Animal Crossing: New Leaf, Mario and Luigi: Dream Team and Zelda: ALBW

I might get a Vita again... But not anytime soon by the looks of it

I'm playing through Virtue's Last Reward on Vita now. Do you know what the differences are?

I bought both.

Vita: was honestly the biggest waste of $ I ever spent. I bought it at launch and has a whopping one game Uncharted: GA and after about 4 months of dust collecting I traded it in for a 3ds XL
Vita: 50/100 First impression was that it looks really nice and I like the control sticks.

3ds: Ive had this for a little over a year now and I have played it nearly everyday. With a massive 130+ hours into Ocarina of Time I can pop that game in anyday. I also have Mario Kart 7 and Pokemon X both fun to play online every once in a while.
3ds: 90/100 Very nice system, does not look as cool as Vita though. Oh yea it has youtube now and it is great also.

3DS, bought a year and a half ago, rate it 88/100.

3ds 70/100
Vita 80/100