And what advice would you give for others debating which one to start with? I am a romance writer, not a YA author. Do you think that infulences the choice ?
If you're not targeting teens, I don't think MySpace is that important. But I would set up both a Twitter account and a Facebook FanPage. They don't take up that much time (I've done both for marketing and PR for businesses), and if you personally do not know how to do it or use them, then befriend a teen or college student who does.
Personally I believe it's easier to reach people using Twitter than Facebook, so if you only have time for one at the moment, then go with Twitter. You already have a blog and a website, so you have something to direct them back to.
What type of publicity is an author is expected to do? Another thread prompted me to ask this question. There seem to be conflicting opinions about what authors should do to promote their work.
If there are conflicting opinions it's because PR or marketing models do not work across the board. Each book is a different product, coming from a different production company, and not only will the production company (publisher) have different requirements but the product (book) will have different needs.
That being said, the few things I believe authors can and should do, even if not required, are outlined in Claudia's post. Aside from diving into social media, work on some grassroots efforts in your local community and see what kind of interest you can generate. Talk to your publisher's PR/marketing team before you do, though, because they will be able to give you pointers to help so you are not going about it blindly. The more a client (author) wants to help a PR team, the more smoothly things go.