God of War is a good platinum, but the final Valkyrie can be quite hard and the Ravens are a horrible collectible.
I would say for a first Platinum, you want something with a moderate challenge and no missable trophies.
I would say Horizon Zero Dawn. It's about 40-45 hours, nothing is missable and it's not overly challenging.
Spiderman is a another good one, about 30 hours and no missables.
Yeah, I agree with God of War, challenging but worth it, a sense of accomplishment. Spider-Man is also not too difficult, just takes some time.