You do know we cant see all your heroes right ?

With posts like these you need to include at least some of the heroes you are considering so those who respond can give you advice on which would be best.

If you are working on Vivian right now, thats always good choice if you`re planning to farm Banshee so cant really go wrong there.

I would say, build the Hunt focused units first and 6 star them. So you will have a faster progress with gear and variety of buildung other heroes. After that and even during this 6 star units that you like the most and enjoy playing. 

I have almost every 5 Star in the game but only use a quarter of them, just because of the meta right now and I do not like many heroes (not my taste or not wanna waste gear for them) what I should not do but still do :D

But always think of that.

Never regret 6 star-ing the hero you wanted because it is always a little progress or a bigger one. And in this game, you dont regret 6 star-ing one unit. Almost all of them are useful for every content.

What I am about to do, is raising up nat 4 stars only because I saw how little my pool is for choosing a hero for Abyss Challange. And I had a lot of fun playing with the 4 star heroes. Especially with "forgotten" ones. If you keep playing everyday , not only daily tasks, you can 6 star a hero in a month :)

Out of the 6 units you posted here-- Gpurrgis the best of the 6 to Promote (imo)

It all depends on who you can build well, depends on your gear. No use to 6star a unit you can’t gear properly. If you have the gear, go for Violet, then Riolet.

Start w/ GPurg since you'll want him as your Wyvern tank. Violet is currently very strong. Then probably Lilias, as she can be useful in both PvE and PvP. Riolet is still a very good DPS, he just needs more protection than many folks want. Maybe consider Adin just because it'll be a little easier to complete her quests if she's 6*, but you can definitely leave that for later if you're not trying to push story. Flan and Kise are good, though Flan's role has diminished significantly, while Kise is hard to build. CMRin is a good but unpopular niche unit if you're looking for a challenge.  

Considering your gold and all the awaken unit u must play for a really long time. 

Like i don't know what u need. 

But for me :aria, pavel, riolet, bbk, violet. 

These are more for pvp option though 

6 star is there for the stat. So just choose unit that benefit from that extra stat. 

Free spirit Tieria  doesnt need to be 6* at all shes only useful in one shot banshee comps. Shes just there for the defense break, Bellona is a better option for that over her in my current experience. 

But yeah aim for hunt/pve story progressing units first like Iseria and Tamarinne if you have them. Gpurg and Clarissa are already your best 2 units to 6* for Wyvern13. Lilias will be useful in Abyss/story

Dont worry about pvp content that $hit might make you uninstall the game b/c of how toxic the meta is.

General Purrgis, Champion Zerato and Arbiter Vildred could help.

You have a few other great units. Just need more time and resources so you can build them all.

... weird... I don't know if my eyes are deceiving me but....is that 400+ million gold.... you don't know who to 6*  but....you have 400m+ gold...not weird at all...