I’m a weirdo, so Massive Chalice.

It has a strange high-concept premise where you are an immortal ruler defending against a monstrous army that only attacks every decade or so. Any surviving individual squad member will only be able to go on a handful of missions before aging out, so you are also managing familial bloodlines to birth new soldiers, while controlling for genetic and social traits that get passed down. I love the uniqueness and big ideas. It’s far from perfect, but you asked for favorite not the best.