I just wanted to let you know of my opinion if Abyss or Apocalypse Dragon is better.
I think Apocalypse is better for two reasons https://100001.onl/.
Elements: Apocalypse has Fire as it's main element so it could be hatched earlier.
Sanctuary Level: So Apocalypse and Abyss are both Breeding Sanctuary legendaries. So are the other 5. But this sanctuary dragon can be bred at the earliest level of them all: You can breed Apocalypse since a level 3 sanctuary.