Not sure there's any individual preference. Price isn't an issue, this will all be award stays. All the properties in Tokyo appear to be ICH, so they're all 40K. For Tokyo, sounds that The Strings won out. For Narita, HI is 15K and CP is 25K, so will balance out "close to Narita" vs. "2nd night back in Tokyo" (plane departs at 2pm, so 10am departure should be enough). Proximity of the Tokyo property to the Shinkansen line would be a bonus, yet if there's a Narita Express just outside The Strings, that would seem to indicate a doable arrival into Tokyo via Shinkansen. Thanks!

[edit] Thanks for the links! Took so long to type up this reply, they appeared after submitting. It appears The Strings is really winning out, given it's proximity to Shinagawa.