JR Pass 7 or 14 day?

Hi.

I am trying to figure out if I should buy 7 day or 14 day JR pass.
I am arriving in Tokyo, spend few days, then go to Kyoto and Osaka, then back to Tokyo all within the 7-day period. After that, I will be in Tokyo for 3 more days, but just locally going around.

From what I can figure, I can buy 7-day pass for the first week. Then just buy metro pass like pasmo or I found that a day pass of metro is only about 600Yen? So even if I buy NEX ride back to Narita with 7 day pass + metro pass, it'd still be cheaper than 14-day JR pass.

Please help. I need to buy the JR Pass soon.

Thanks.