At Capcom's "Captivate" event, the company announced an unsurprising but nevertheless nifty feature for Street Fighter X Tekken. Once the Vita version hits this fall, you can play cross-platform against PlayStation 3 owners, via Wi-Fi or 3G. We would say to play 3G at your own risk against console owners with months of experience and access to fight sticks, but that's your prerogative.
Other newly announced features for the Vita version include touch controls, local and Wi-Fi multiplayer with other Vita version owners, and the use of Vita's Near function. It seems like the presumably cheaper Vita version is the one to get if you haven't already plunked down your cash.
Capcom announced a long time ago that downloadable content will be cross-platform, so any extras you buy with the Vita will work on PS3, and vice-versa. This also makes a bit more sense of the extra characters being on-disc on the console versions, since it will allow them to play with those characters intact cross-platform without downloading a patch. Then again, the company's PR handling hasn't exactly calmed tempers.