The units (aside from the ones I told you in shoutbox for your subjugation) that you will want to level are the following:
top priority:
plat & blacks: Minerva - Adele - Camilla - Thetis - Garania - Spica - Marius - Lilia - Bashira
golds: Iris - yuyu - katie - bernice
middle priority:
plat & blacks: Sophie - Lyla - Marr - Claudia - Imelia - Zenobia
golds: Fedora - mehlis
low priority:
plats & blacks: Aisha - Liana - Hina - Waltz
golds: Zola
Male-only maps:
Julian - Garrett - Cyrus/Barbie - Vincent - Robert - Conrad
potentially useful (some of them are post-AW): (those that have not been mentioned above)
Victoria - Berna - Shizuka - Viera - Monica - Betty - Stella
not mentioned = more or less useless.