Imo the decision is quite easy, if u want "real" gaming, take the NGP(psp2), if not then go for a good Android phone. Only consider the Xperia Play(playstation phone) if u really need these physical buttons... because it basically doesnt really have anything else to offer lol. Any good Andoid will be just as good for playing (ps1)games (just without the physical buttons..)+have other advantages.
ive seen that there will be a new application for mobile devices called: playstation suite : you can play playstation games on mobile devices,
You can do that already with "psx4droid".
I'm looking forward to the playstation suite as well tho, as its time for some improved/better ps1 emulator...
Will be interesting to see how the NGP and Xperia Play will be priced, atm I dont see any good chances for the Xperia Play unless it really has a good price coz it doesnt offer enough imo (physical keys yay... but nothing else setting itself apart from the competition, just another Android, which can run a ps1 emulator). Thus I'm more interested in the NGP as I most likely wont switch from my Galaxy S (at least not for a x-play^^).