I asked my self this question earlier today and thought long and hard about it. I still do not have an answer. Suppose you were only allowed to operate one website for the next two years. What type of site would it be and why? I think this could be a valuable and intriguing discussion, especially for those of us who tend to spread themselves out too far.
A politics blog, so I could rant and rave all I wanted, without having to worry about my other sites backlinks, ranking, and bandwidth...
porn sites get quite boring and quite tedious after a while.... i have 9 of them and it's never ending battle against content copy and pasters and then there is the traffic sourcing (esp if you are doing tgp/mgp submissions). I've actually made more money from google adsense in the last 14 days than I have in the last 3 years of adult sites (go figure)
a (medical) health forum... i am a doctor i would discuss many things like diseases and prevention, diagnosis, life quality, etc
I think if you are only working on one site then it should absolutely be on a topic that you know and love! I have run loads of sites that I have no interest in and usually have to outsource the work on sites that I find boring (but that I know will make me money!) If I could only pick one, it would be a private membership site for indie musicians! (A project that I intend to set up when I have time!) Chris