As far as i know, none of them can be considered as core. Of those, i would start with dark team.
1. Cerberus is the best probably due to her guaranteed def debuff.
2. Not sure about this tbqh. Light is popular due to number of crazy himes here, but if you didn't manage to put a full-packed team of those, pretty sure it will not be any better than other elements.
3. I think it's mostly due to a lack of heal, but they got Nefertem just recently, so it'll probably changes. Also there is Thanatos awakening soon, tho i've no idea, what her aw form will be.
4. Try looking in there for some ideas https://harem-battle.club/kamihime-p...s-element.html