if you're dead-set on using a handheld, the gp2x is pretty rad, but they're kind of hard to find, can get expensive, and you're kind of shafted if anything breaks on it.
the psp is cool because they're cheap and everywhere, but it doesn't run lgpt natively, so you have to mess around with that to get it to work.
i just use a pc. all your samples are right there, there are more external audio connection options, you don't have to transfer anything back to upload it, etc.