Is JR Pass a good choice within Tokyo?

I will be in Japan 15 days total. I plan to get a 7-day JR pass for the travel I will do between cities. I will be in Tokyo for 8 days and I am considering buying the 14-day JR pass instead of the 7-day pass. The subways and train lines are confusing to me looking on a map. Can you advise me as to whether I should get a JR Pass to cover my days in Tokyo, or would it be better for me to get some other kind of local subway pass, or just but a pass each time I take a subway individually when traveling within Tokyo?