The best keywords are related to your content. If you are paying for keywords you would want to probably pick ones that more people would search for. It is also advisable to add in keywords that may not be as possible because they will put you higher in the rankings.
I would recommend changing up some keywords and then seeing how it affects your traffic. Also, Google Analytics has a feature that allows you to see what keywords brought people to your site. This might be helpful as well.
