Sony PlayStation Vita or Nintendo 3DS: which?

I've never thought myself to be a heavy gamer; heck, most days I'm content with a little "The Sims: Freeplay" here, or some "Ridiculous Fishing" there, all on my more-than-capable iPhone 5. Nevertheless, I have decided it's time for some higher-level gaming.

Since I'm still very much into handheld gaming - as a postgraduate student, getting the whole TV gaming experience probably isn't in my best interests right now - I'm stuck between the two obvious choices: the Vita or the 3DS?

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OR

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My natural bias toward Sony hardware notwithstanding, both (as shown above) are excellently-designed devices I would be more than happy to carry about in public. Dare I say that red 3DS XL is sexy? And they both have titles compelling enough to argue each of their cases, but I can only choose one. While I have always longed to play the 2nd and 3rd MGS titles, which are on the Vita, the 3DS has something I've always loved since I was a kid: Mario Kart Racing!

Decision time is fast approaching; I intend to get one of them as a birthday gift to myself in two months' time. Does anyone here have both? Or which do you think is "better", albeit marginally? I would love to hear recommendations. Thanks for reading.