If we're not counting digital, the 3DS by a long shot, thanks to it's backward compatibility.
Ignoring physical backward compatibility, it's close, though I still prefer the 3DS (Vita's a bit more niche, but there's some really good stuff there too).
Factoring in digital, probably the Vita. There's tons of (J)RPGs on PS1 and PSP, and Vita gives you digital access to most of these. 3DS has some good stuff in it's eShop, too, but 3DS Virtual Console is still very lacking.
Personally, I prefer the 3DS, since I don't like digital. That's why I bought a PSP and a PS1 for their respective games. My 3DS has ultimately made my DS lite useless (except for the ability to play about 3 of my import games that the 3DS can't play), and thus I'm factoring in DS's library, too, while the Vita has to life off of it's own available-at-retail software.
Nintendo Network ID: domflo
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