I decided to post my question here rather than starting a new thread.

I am having trouble deciding what Legendary soul to unlock next, either for main use or for access to their extra abilities.

I've only unlocked Arthur (since the game starts you at Lancelot, I subconsciously unlocked Arthur chain) and Andromeda. My main element/party is dark and I primarily use Andromeda with Soothing Breeze (regeneration all) extra ability, Satan, Amon [Unleashed], Beelzebub and Mephistopheles.

For primary buffs/debuffs, this party only gives me:
((A)+20%)Defense Up All - Andromeda
((A)+15%)Attack Up All - Beelzebub
((A)-25%)Defense Down - Amon

I've read a number of topics/posts that talk about Mordred/Black Propaganda, D'Artagnan/Sniper Shot and Siegfried but still can't decide what path next to go down for myself. I would still need 700, 800 or 1000 soul points respectively to unlock all remaining in their chains and I only have 520 Soul Points currently. I am Rank 54 and started a few days into Quetzalcotl Raid Event. Soul points are at a premium right now.

I feel as though I'll always need Andromeda with Regen as my soul/healer for lack of a dark healer until Osiris/drawing a SSR healer but any veteran advice/feedback in what Legendary Soul/Extra Abilities I could benefit from sooner rather than later would be greatly appreciated.