I'd awaken Elizabeth or Thetis as they will be really useful on this event (reasons are mentioned in post above)

But in general it's really up to you. Check all awakening passives (with an insight in skills for future) and decide which one will work best for you. I'm currently AWing Elizabeth but im short on money <.<

Peronally, my aw choices were like this in that order: Sophie cause she's my waifu, Thetis cause op sprite D: , Spica cause everyone said so.., katie for def buff, cellia for spirit buff, Healers Iris and Camilla for drop heal, and then rest of my units just cause either they were either black, or i used them as my very very often