I don't write longhand very often because I can't keep up with my thoughts that way -- I have enough trouble on a keyboard, and I touch-type pretty fast. On the other hand, writing longhand does make me consider each sentence more carefully, so I don't have to scratch out as much.

Mostly I wrote prose on computers and poetry on paper. This is probably because poetry is more of an aesthetic endeavor for me, and I do take the time to consider each word and phrase at some length. I also like having hard copies of each revision, and poems, unlike stories, are short enough that I can do that. I do a fair bit of world-building on paper as well, because I like to play around with lists of names and words and I don't like the way those look on computer screens.

I wonder if any writers are completely rational about their particular processes and idiosyncrasies?