If you're a gamer, the chubby one sits in your hands better. I have a slim and 200+ gigs of games on an external. o:

Just makes sure after you mod it, that you pull out any UMD's out of the back. There's no need to ever have one in there again. Oh.. and a .cso is a compressed .iso. Always format your memory stick in the PSP so that it creates the proper folders. Movies go into the VIDEO folder and all games .cso and .iso go into the ISO folder.