It's a bit of a difficult choice for sure, but I'd probably go with Amonkhet because at least the gods there actually care about the mortals.

7272567
Up until Bolas pulls the trigger on the entire plane, anyway. And even then, the entire society is designed to grind out the most capable fighters possible and then kill them at their peak to make optimal Eternals.

If I had to choose between the two, I'd go for the one that isn't a city-sized zombie factory.

Theros. Hands down. No contest.

Go to Theros, convince everyone to be an atheist, kill all the gods at once! >.>

Xenagos did nothing wrong.

7272800
Why not convince everyone that you are a god?

7273644
Xenagos is what happens when a party pony turns to the dark side.

7275430
Kiora tried that. She got a neat fork out of it, but it didn't go well for her otherwise.

7275482

Kiora tried that.

So did Xenagos. The difference is that Kiora tried to convince them that she's one of the already established gods, while Xenagos convinced them that he's a valid new player in the gods game.