I write using tab software. I usually tab everything out in Powertab or Guitar Pro first, write the bass, anywhere from one to three guitars, and drums. I decide beforehand whether I want a part to be distorted or acoustic.
I never really liked writing stuff by sitting around and playing a guitar. I mean, you come up with some cool riffs and things, but I find that, for me at least, it's easier to put thought into these things when it's just me and a computer.