S1 heroes in near-constant use in my case:
Khagan (cb) - particularly events and towers
c-Joon [not that different from Joon normal]
c-Rigard (seldom Rigard (cb))
c-Melendor or Melendor (cb)
(Leonidas and Lianna get occasional use, as does Kiril (with and without costume))
Sartana isn’t bad, and just leveled Domitia’s costume, though I haven’t used her yet.
To be honest S1 five star heroes diminish in value with each new family of heroes being released by SG.
I now see very few naked S1 heroes on the battlefield- but I suppose that depends on your alliance ranking, your level, what you want to focus on in the game …
However costumed S1 five star heroes continue to be relevant
And others too, but probably used less often
The most used costume on defense I can see is kadilen. She is used even by the biggest of whales
On offense I think Marjana and Leo costumes (both EDD for 3) are the most impactful, for top players.
As you move down the money ladder other heroes get used, mostly the snipers (often just the costume bonus) and Viv.
After that you hit the stage where people simply play with what they have And costume (bonus) S1 is always going to be better than S1.