We recently had a conversation with a plumber and asked him about PEX. He felt that even though for installation it had some advantages, he did not want to move away from copper pipe.
One of the reasons he did not like PEX was because some insurance companies were hesitant about it being used. It appears some types of PEX might leach chemicals into the water. As a plumber, he did not want to worry about unknowingly installing an inferior manufactured PEX and later getting sued for it.