I often have a hard time choosing the best tags. They do matter a lot though. We should always maximize our full potential use of the tags as well and use all 5 so that we can give ourselves more exposure. I like to look at the less visible tags more often than I do the bigger ones. The bigger ones have so much content coming through all once, the post has gone down the line within seconds.
@magicalmoonlight You are right on the number of tags to use as they will determine how widely the post gets coverage. The key is to ensure relevance to the tag the post has.