Compression fitting will last longer than copper. If a copper fitting is done wrong it can pit. I'm going to be honest here and tell you I can't find sources for this but I thought I've seen it before in research -

Copper lasts 50-60 years. I believe that's type L which is used in the wall in homes in the US. The skill required to create a high quality copper joint takes time and a person may still make mistakes. A PEX compression fitting is basically just closing a tool. The probability of mistakes is lower.

I'm not familiar with the possibility of contamination in pex, is this due to the material?