Ms. Marvel Vol 1: No Normal, by G. Willow Wilson et al
To a happier part of the 2015 Hugo discussion. I really enjoyed this graphic story about a teenage Pakistani-American girl in New Jersey who acquires super powers. It deftly combined a number of familiar tropes, from Buffy and urban fantasy on the one hand and the increasing literature about being a non-white kid in a new and largely white country on the other, and was also very entertaining. In this category at least, I may have a tough choice.