Gigamesh or Istar?

Ishtar is basically a shittier Gilgamesh.

short answer 90% of the time gil.
Long answer, she can be better if she get her right chain ageinst non servant fight. Unreliable.
still she is better for support.

I like to think of Ishtar as having a larger range of damage than Gilgamesh with a higher ceiling IF and only IF the cards line up perfectly with her skill cooldowns. Gilgamesh however, is the more consistent servant. He is much less reliant on RNG and having his skills active, as much of his incredible power is tied to his absurd NP.

Tbh you could easily google this. Almost all of the time people will say Gil. Currently they are about even, Ishtar maybe a bit better, but once Gil gets all his strengthenings he is much better.