if you got the budget buy both... at home when you wanna full concentration playing on a bigger screen then play 360. if you got too tired playing on big screen then play your psp while lying on your sofa... (like me lah). sometime i got too tired playing 360 then while taking my rest on the sofa, swtich to psp.

still it depends on your lah. i like my psp too because it follows me into my lecture's hall