Need some help. PSP or PS Vita ?

Hey, i want to buy i psp but the ps vita is out for now. So i need some advice to choose between them :)

• First, Which is better? (Just in case)

• Second, Can the Ps Vita play the Psp games? (I read something than i can play downloaded game? Need some tips on this too.)

• Third, What is the difference between price and quality?

For now, these are my "main" questions. If you got some advice for me just go ahead. I'll edit if i got some other questions.

*P.S I made i post on /r/gaming but i didn't receive quite response.

Thanks to all in advance !!