While they're currently experiencing some pretty serious slowness and glitchiness due to sudden popularity, I'd argue http://lemmy.world is the best Reddit alternative we have at the moment. It has a fairly large variety of subreddits (ie communities), and their user base is, for now at least, fairly active.

I just hope they can fix their numerous server issues before they miss their window of opportunity.

Is there an article or thread that talks about the issues they are having?