For PVE, i vote for tamarinne. ive been using her a lot in abyss and hell raids. 

Tamarinne for sure.

@SirJay what lvl r u in abyss? and what is your max team cp?

Currently stuck at 87 abyss, I think I’m around 360k

Tamarine, Sigret, Violet and maybe Shadow Rose either one these probably a good choice. I am not a pro player but i think Tamarine would be useful in some PvE Contents and Sigret for Wyvern perhaps and Violet and Shadow Rose for PvP if you intend to focus on PvP. But this is just my opinion. :P

for PVE:

Tamarinne 

Angellica 

for PVP:
Sigret

Shadow rose

Violet

Warbalt (Youtuber) gives the advice 'build your units around your available gear, don't build gear around your units.'

So with that in mind, it depends what sets you are farming, and what artifacts you have at high level or high limit break. Have a decent Reingar's Special Drink? Awesome. Invest in Yuna and watch her destroy everything. Max level Moonlight Dream Blade? Stick it on Violet and you have the perfect assassin for all those water units that break game balance.

But JUST from looking at your units, you only have two elements covered when it comes to bait units (Krau, Lilias - maybe Kayron and Ravi count too). So even if you don't want to invest in an earth tank, a light one would cover your ass against a lot of defence comps (Kikirat or F. Maya are best).

If you face a GvG defence team like Charles, Assassin Coli, Kayron, you can use something like F. Maya, Angelic Momo, and a water DPS unit. This funnels the Kayron and A. Coli damage into F. Maya who you can keep healthy.

Tamarinne