I picked Solael because I’m playing a shieldbreaker majoring in fire, and Solael is associated with fire/aether damage in-game (witchfire etc). But by faction quest #2 you find out how much of an asshole he is 
TBH looking at the faction vendors it’s not actually all that clearcut, so I’d say choose based on whatever RP reason works for you
Can someone confirm that whichever one you chose, you can get reputations (rather easily, which means not having to go to another difficulty and start over… like kymon or the outcast) for all of them on the same character in the same playthrough ?
(I’m in ultimate, didn’t try the DLC yet, and I was afraid to start it and f*ck it up with the reps and the augments and all…)
Just pick whichever you want to rep up the fastest. OR alternatively, pick Bysmiel for the sweet Aetherteats Malmouth poster girl
Confirmed.
Story quests will give you a big chunk of rep, and Eldritch Horrors enemies (which are plentiful) and bounties also give rep for all three factions, so it goes up pretty quickly.