I am working on three separate projects that are at the same time very similar. Three online magazines. One about fashion, one about art, one about music.

What is the best SEO approach: one website, or three websites.

My guess is one website, because if one gets successful, the three others will benefit from it.

If I am guessing correct, what is the best approach to this: subdomains or directories? I would guess directories as I seem to remember that the keywords are given more weight.

What do you think?