well a b-sides best is impossible but anyway xD let's see
if the american albums also count i'd include

Amai Wana
B & C
Kotoba ni naranai kimochi
Hayatochi Remix (if it doesn't count Hayatochiri)
Deep River
Tokyo Nights
Animato
Hotel Lobby
Making Love
Kairo
Celebrate
Take 5
Merry Christmas Mr. Lawrence - FYI
This One (Crying Like A Child)

if This Is Love and Fight The Blues count, i'd replace them with Making Love and Take 5....
and hikki should resing/rearrange some of those old songs :D would be cool...
AND she should include some new bonus songs so people buy it :P i already imagine the bonus song title "Ode To Kumachang"