Does the Airbus A320 or Boeing 737 have better resolution screens in the cockpit?
B737NG DUs (Display Unit) have a resolution of 1152x1152, as per the maintenance manual. The display size is 18x18cm, making it around 163 PPI.

I have found a source that claims A320 PFD has a resolution of 768x768 and the display size is 158mmx158mm, making it around 123.4 PPI.

I imagine B737 MAX is using the same 15.1" display as the B787. In this case, the resolution is 1400x1050, and the PPI would be around 116 PPI.