All of the Pre-Neo SNK arcade games that are available on the PSN work on the Vita save for 1 or 2 (POW, Ikari Warriors, Alpha Mission, Street Smart, Ozma Wars, etc). The PSN Neo Games - such as MS3 and Magician Lord are available. Any Neo ports that are PS1 classics, such as KOF99. PSP games that are downloaded will run nicely too, of course, such as Metal Slug XX and Strikers 1945 Plus.
I generally like the Vita better, for the screen and the D-Pad. I also have one of these for added comfort, which I would highly suggest: http://www.psvitahub.com/2012/02/ps-vita-trigger-grip-attachment.html
new one has shittier screen . so get the older one
WHOLLY SHIT I have a metric ton of available downloads. 8 years worth of purchases and PS+ goods. Looks like the largest mem card is 64GB but it's not officially sold in the USA. Has anyone tried one?
PSP games on vita look great IMO. I def prefer playing on the larger screen - and the scaling is done way better than say playing DS games on 3DSXL.