I've got the same dilemma. I have Apple delivering on Friday and Amazon (hopefully) delivering on Saturday... I was going to not open the Apple one at all and just return it boxed but it doesn't seem like they care either way?
I should probably mention, this is my wife's phone so it's really up to her 😂 but I'm assuming she'd prefer double the capacity for £150 less...
I would not open the Apple one, to save you looking like a peasant when returning the phone to Apple with opened box and made up excuses. It’s better to return an unopened box and tell them you had a change of heart.