Sartana, because her ability is offensive and to make the most of it she needs to be as powerful as you can make her.
Kunchen’s ability is just as good at 3/70 as it is at 4/80 (assuming it’s maxed). Leveling Kunchen will be purely to let him survive longer, that can wait… Besides, you already also have Tiburtus maxed for titans, and Sabina for a purple healer. Also, your defense team would greatly appreciate having a strong offensive punch, which Sartana will provide.
tl;dr, Sartana. She’s arguably the best classic 5 star.
Wouldn’t it make sense to max a sniper for a first 5star though? I agree that Kunchen’s Def- is great with all those heroes, but none of them are leveled. Sartana would produce more immediate results in terms of clearing campaign content and raiding.
Edit; I misread, I noted that you have dupes of Frida and Evelyn that are leveled
Oooh if Frida and Evelyna are 1 mat away, then I would actually go with Kunchen for the reasons Fravitz mentioned, def- benefits wide range attackers a lot.
I have him at 3-70, the only reason he’s not going to have my tabards right now is that I’ve got Hel and Ariel. So, Hel was my first maxed purple, and Sartana will be my second.