> I don't know which to get Casio or iPaq, which one runs MAME better/faster?
>

iPAQ is faster but has annoying button problem where you can't press more than one button at once. Only button that can be used together with others is an action button (that is when you push joypad inwards) Because of this, diagonals don't work and you can't jump and shoot for example, if you don't use some weird key configurations. Many games/emulators today use virtual on/screen keys so you can press your screen instead of the buttons. Too awkward for me. I went with casio EM-500 and never regretted. Casio has also by far best screen with very vivid colors and great contrast. iPAQs screen is more visible outdoors though.