Realistically, this question is incomplete. My mind jumps to "pu" as an intended "push", and even then, the rest of the question is missing. I also thought "pu" might be an acronym for "permanent use", as in registering something to the select button, but I believe I was giving the asker too much credit there. Ignoring the second possibility, it becomes a question of personal preference. I pu the A button all day long, but maybe that's just me. Oh yeah, and googling "pu button" doesn't point to anything intelligible.
a255 I have no idea what you're talking about.