I have an old Rheem powervent I will replace with a BradfordW powervent, they are both 50 gal 40k btu. My house is plumbed with polybutylene joined with copper fittings.

The old heater has PB running direct from the hot outlet. Should I run pex or use a certain length of copper pipe to get to the PB? Will the hot water degrade the Pex?

When I join the pex or copper to the PB I see there are sharkbite press in adapters and pex/pb copper crimp ones. Is one more durable or preferred over the other? Thank you