They’re both addictive. I’ve never really done either one, so I don’t know which is more addictive.
Pashuteh Yid, I don’t see where anyone has answered your question about what’s so bad about Facebook. Besides the obvious bitul zman, teens in particular connect with all kinds of people who are not the best influences. They “friend” people they don’t know and are exposed to all kinds of shmutz. Because it seems to be somewhat private, it lessens inhibitions, in a similar way to how the Internet made pornography more accessible. Yes, it can be used to help families keep in touch, but that’s not how teens use it. I think if you ask anyone who works with at-risk teens about Facebook, they’ll have a very negative opinion.