What niche should I choose for my community?

Your niche should be basically a mix of something you are passionate about and something you are good at. You should have long-term interest in the subject and want to become an expert in.

But do not let this point stop you! If you are not sure about the right niche, just start. Pick it, register a free account, launch and figure it out as you go. You will recognize shortly whether you like to build an own community or just join an existing one (if there is one that suit you).

A lot of community starters have this problem of pondering about the niche, that holds them back for even starting a community at all. My best advice, try the niche out, skip if not appropriate and try the next one.