imo Kanno > Sawano.
I like her huge diversity of music over his focused digitalized sounds.
Some other composers I only have limited knowledge of, but I've had a great first impression of:
Toshiyuki Watanabe - Space Brothers OST - Orchestral - moods: exploration, grand discovery, casual whimsical.
Tatsuya Katou - Samurai Girls OST - Orchestral - moods: battle, whimsy, focused on Japanese traditional instruments
Tanaka Kouhei - Hyouka - Orchestral - mood: "short-stories" of many themes; mystery being the primary
Choro Club & Senoo Takeshi - Aria: some of the calmest piano and Brazilian-style guitar playing
Nomi Yuuji - Nichijou - Orchestra - very great story-telling comps... think silent film comedies.
Michiru Oshima - Tatami Galaxy - Orchestra - classical orchestra almost... retro-Japanese style of pop
Kousaki Satoru - Monogatari - very experimental sounds