do you plan on leveling up loremaster (civil ability that allows you to identify objects and examine enemies for info) on someone? if you aren't doing it on fane then sebille is a great candidate because her elf racial bonus is +1 loremaster
on the other hand, i do like lohse's story quite a lot and she works great as an enchanter, especially when you get savage sortilege and take advantage of her +5% crit chance
overall i'd lean towards lohse for her story. sebille's is good too but it doesn't last quite as long through the game as lohse's does
