It does take a brave man to bet against Nintendo, and I think I also agree that the 3DS should win sales wise, but I don't think it'll be as clear cut as the DS vs PSP - albeit that's more because I simply see the 3DS not having a hope in hell of selling like the DS, whereas the PSP2 looks well poised to do similiar numbers to the PSP.
While Sony so far has shown the PSP2 similiar to doing the PSP strategy, there are upsides to this. They'll see alot more software support (If it's true that for eg Lost Planet 2 took 2 weeks to port to the device) and it does allow them to create software that distinguishes itself from the rising phone games market. It's worth remembering that not every game is going to be an Uncharted or Killzone, that the Android IoS will lead to more 'portable' style of games priced appropriately and that Sony will inevitably 'show off' the big, graphical behemoths first as that's the systems biggest selling point.
Further to this, I think Nintendo's current strategy with the 3DS can be critiqued as similiar to the PSP's anyway. Unlike the DS - which sold on having a touch screen and being accessible to anyone, the 3DS's biggest selling point has been 3D - something that makes games look prettier... just like the PSP2's biggest selling point. Further to this, outside of Nintendogs 2, their software line up is very 'console centric' too - Zelda:OoT, MGS3, Street Fighter, Dead Or Alive, Paper Mario, Starfox 64 etc...
I think the PSP2 has potential but whether it can hit it depends on what Sony does from here, and how they treat the device in the next 2 years. For me the PSP's biggest downfall is after a solid launch, software support simply dried up and they didn't have enough to keep the userbase enticed, so eventually people stopped buying software (Obviously PIracy didn't help). Sony need to consistently release games that actually get any marketing, we'll see.
I can envision bomberman and pilotwings being great for on-the-go gaming.