The Vita version of Phantasy Star Online 2 will have the portability advantage over the PC release, but it'll also have one serious disadvantage. Sega revealed that it plans to release the handheld multiplayer action RPG in 2013. The PC version is still slated to begin service this year.
Andriasang has the first screens of the Vita version, which reveal a game that looks as if it could use that extra development time -- the screens are a bit rough. Sega said that the Vita game is just 10% complete, so presumably it'll look nicer as it approaches completion.