You eat your psp.
What do you want to do with your psp? Play isos? change the icons?
change the look of my xmb and bootscreen n stuff like that
go to 3.03OE
there are higher versions, but the additional features of the higher firmwares are retty minimal, and you won't miss them. and 3.03 is the highest for cheatdevice, and there are a lot of 3.03 xmb themes already made.