I've been toying around a bit with Black Sun, i might get a party in the near(?) future.
I can't decide on the leader. Sophia and Promethea are in for sure, so:
Clover:Pros: 1)Can get buffs from Promethea (Rebellio even twice) and Sophia's Offensive Analysis; if he does manage to use Prometheum, everything he touches will most likely die (or soon will) with 14/6 and an additional die. And that's without even counting Focus, Gnosis or any advantage.
Cons: 1)If he is already engaged it could take at least two turns to use Prometheum, assuming that you have to dodge/disengage/attack to Throw.
Lynn:Pros: 1)Cheaper.
2)She can take Fate Clock to change the Doom counter to everything positive she wants (Shield isn't bad to get 4 armor, Haste is also very good), or take Supernatural Weapon and Piercing Weapons for some extra hitting power.
3)The sickest thing about her is that Sophia can use Defensive Analysis on her to raise her Defense to 17(

) when using Mirror Image which means that enemies with attack less than 10 will need at least an 8 to hit her and every time they miss, she hits them back.
Cons: 1)Hits much less than Clover with her basic (reactive from Mirror Image) attacks unless she turns the Doom counter to haste so she can use X-Calibur, at least once.
2) She is not Clover

(aka lacking coolness).