Even though the analogue camera for Monster Hunter Freedom Unite with a Vita isn't true analogue, and only replaces the left/right d-pad buttons on PSP, I find it much easier on my thumb than 'the claw' with PSP.
I also much prefer the Vita d-pad. Other than that I can't think of anything outside cosmetic stuff- personally I prefer the Vita interface with it's 'launch' pages for each game, so I must have clocked up hundreds of hours playing PSP games on my Vita by now. To each their own, really.
I've seen people argue that PSP battery life for digital games is better, so there is that, although personally my Vita has never run out either. I use it every day for about 90 minutes each way on my commute, and charge it every two days, so it depends on your circumstances I suppose. A PSP might be better if you have a long flight, although these days I carry a portable battery pack for the various gadgets I'm using when I travel, and a USB cable for the portable I'm using when I'm not. I think I've charged my Vita off of hotel tellies, computers, trains, aircraft, pretty much anything! Proprietary chargers just seem awkward and unnecessary for gadgets these days.
Yes! Playing on Vita is much superior.
- Resolution is exactly double, so games scale perfectly.
- You can remap controls to the second analog, meaning you can, for example, often get camera to map to analog, or convert compass button shooting to 'dual stick' shooting.
And comfort - once I started playing on Vita I found it really hard to go back to my psp. So much so that I've re-bought probably 30 games over the years [I had made a secondary 'psp' account for ease of use years ago - ps+ plus single accounts on vita effectively made that account pointless.
Thanks!