get Sol.
you have LTsuku, who is the top priority light hime. Next in line would be Sol, she's perfect for any team too, can be useful to dark if needed, moreso than Osiris, other than the fact that she's off-element. good for thunder/wind as they don't have a SSR healer (yet)
Plus, Sol gets her awakening next month and becomes fucking crazy OP.
Osiris is under powered for a SSR, she really needs an awakening in DMM...
Thanatos can't be chosen w/ miracle ticket (Amon U 25% DEF debuff becomes C-frame in a future update a year away.)
Though Satan will get her awakening in a few months and have more debuffs(dark resist down to enemy.)

but... well, Sol sounds like the best option.