Oh man, this game looks goooood. So much variety, and it seems like they put some serious though into which girls gets which outfit/scenario.
If you don't have either of the handhelds, dive in for Vita. Better hardware & capabilities, and there's probably a limited chance any further games will be on PSP too.
Consider this [/REM]: a PSP costs 95 euro, whereas a PSP Vita costs 285 euro! For that 190 euro difference you can buy the LE version of the game and any accessories (hint: 1/153 Official Guidebook) or other games you might want.
In addition, a future version of this game won't release until late 2013. The PSP Vita will have come down in price and/or there will be an upgraded version on the market by then.
Just playing the devil's advocate, I know prices vary a lot depending on where you live. In my case, I simply cannot justify paying an additional 200 euro for a Vita.