I have 4 fully leveled 50s, Lianna, Vivica, Sartana, and Marjana. For my blue, would Magni, Aegir, or Athena be the best fit with the other 4?
In a vacuum I’d say Athena. That said, your team will grow stronger faster if you level up a couple of 4* teams.
Athena is far better at titans and very strong on raids as well. Since you have a healer, she would be the top choice with Magni second.
Athena sigh (I didn’t pull her so I’m a little bummed) she’s really amazing for Titans and great for attacking, so I’d assume great for events and quests also, so her first. Too many snipers, so as much as I love Magni, I’d hold off on him for a bit. Aegir after Athena for a solid tank. He’s no Guin, but he’s still good. I think he’s one of those heroes that you’d have to work with for awhile first to decide how best to use him and if he’s worth the mats for you, since he’s very niche. If you decide you don’t like him though, then Magni, but only after Athena.
Definitely Athena. She is a very solid hero.
There’s an understatement! Just looking at your 5* (and I’m hoping you have a nice bench of 4* heroes!), Vivica has an excellent defense buff, but you don’t have a way to debuff foe’s defense. That’s Athena.
Between Aegir and Magni, I’d have to give the nod to Magni. Anchor rates Aegir highly, but I think it takes a bench of excellent heroes to fully benefit from him.