I've had quite a few issues now, some big and some small.
Example:
My family live abroad. When married, I routinely took the DC there for 4+ weeks in summer school holidays. I want to do that again once Covid restrictions lift. ExH now says it's not in their best interests to go 4 weeks without staying at his. They will still split the summer holiday 4/2 weeks (4 with me). I can't tell whether his perspective is reasonable or not.
We also disagreed about secondary school for our autistic child. I wanted special school, he wanted the closest school so I didn't move and make it harder for him to have DC overnight. He has Fri/Sat night EOW. I think the school isn't a good fit and our DC will suffer with worse academic results than at a special school. But I see the benefits of living close to both parents. How do you actually decide what's the "best interests" though?