There’s a good discussion of Marjana v Natalya here:
Personally, I put Ares top, with Marjana second. Behind these, the other 5* all have a case to be made for them and are solid team members (except Guardian Kong, who I wouldn’t waste blades on, let alone rings). If you like fast heroes (good case for that), and you don’t have Marjana, then Natalya or Kestrel are the choices. Between those two, I think Natalya is the better option–although there’s a case to be made that, in a post-Zeline world, having an all-business no-buff hero like Kestrel is a great option. I expect that Kestrel will be available again in a few weeks.