When an article is submitted to a conference or journal, is it better to use British or American spelling? Does it have to be according to the conference or journal's style (based on where it is being held or who hold it) or is it up to the writer to choose and stick to one style?
I'd think that the writer wouldn't be expected to change his or her writing style based on the style of a particular publication. I've seen both styles in the same journal before, so I'd suggest writing at your comfort level.
When I write papers, I usually try to write in American English. I say try because not being a native speaker (I'm Belgian), i have a natural tendency to mix up stuff. So when I'm not sure, I take a dictionary and look up the possible spellings and will settle for a consistent choice, which is most of the time American English.
The most important is to be consistent.
The only time you'd have to choose is if you're submitting to a journal or publication that has a list of writing standards to which applications must adhere, and one of their standards is preferred spelling.