What an interesting question, Chris!
For me, the answer is both. I "write to order" when it's pay-the-grocery-bill time. It doesn't always come easily, which is why I don't always make my deadlines!
Fanfic, however, is being "ordered to write" - when I have the time and the leisure and the desire to write. I can let ideas simmer in the back of my mind and play with them whenever I want. When I wrote "SuperKal" (the filk that took me longer than any other, as of this writing), the first two lines of the chorus popped into my head when I was walking down to do some shopping. I spent the next several weeks working out the chorus in my mind at odd moments, until I was finally satisfied. Then I sat down and did the rest of the lyrics. I couldn't do *that* with my regular work if I ever wanted to get paid!
Fanfic writing is much more fun. Much easier, too. Of course, it doesn't pay the bills, so I can take as much time as I want to get to it... as long as the readers don't lynch me first.
