PMs should always lead voice of the customer (VoC) programs
While PMMs need to have their ear close to the ground when it comes to customer feedback, it's ultimately the PM who will use the feedback to make product decisions. Additionally, PMs should never be in a situation where product feedback is "second-hand" or being prioritized by someone who doesn't own the roadmap.
Some best practices that helped my teams create a collaborate cross pollinating environment are:
It’s a joint decision between product management and product marketing at Square. In general our PMMs tend to have more ownership here. They will lead competitive analysis and commission qual/ quant research to inform pricing decisions.
That said, from what I observed, when you zoom into the specific PM/ PMM pair, it really comes down to whoever has the expertise and the respect from the team to make the right call.