psp, only because i have almost all my favorite genesis, snes, nes, gba games on it.
as for actual retail game quality... def jam, gta, lumines, there are some good ones for psp.
and for who said
"The DS Lite is a durable little handheld with a quality build and quality games available for it...and it's cheaper!"
i have to say, there was a pretty decent amount of lites that had that bad shoulder area that cracked under normal use, it happened to a friend of mine.
i love them both, but only own a psp, have to use my nieces DS for wario... which is fecking sweet.