Hello rkpatt,
Non-profession plumber here. Been researching this myself for about 2 years now, but I have not come to any conclusions yet. Between the two options, my guess would be the Crimp copper rings with a mechanical tool (just easier if a tool exist). But I like the Expansion System (like Uponor ProPEX and REHAU Everloc+) because the fittings do not reduce/restrict flow by reducing the diameter of the pipe. The diameter of the fitting is small than the pipe in the Crimp and Clamp Systems. Do some researching on the fitting (brass vs polymer). There appears to be some lawsuits regarding the brass fitting and dezincification. I believe REHAU exited the residential market around 2009 because of this problem.
Check out this from HUD at huduser[dot]gov. Good information.
Design Guide - Residential PEX Water Supply Plumbing Systems:
https[collon]//www[dot]huduser[dot]gov/portal/publications/pex_design_guide.pdf
There is a section that discusses "Material Properties".
* Temperature and Pressure
* Flexibility
* Noise and Water Hammering Resistance
* Resistance to Freeze Damage
* Chlorine Resistance
* Corrosion Resistance
* Ultraviolet (UV) Resistance
Just some thoughts to consider. Forgive me if you are already aware of this.
UV light destroys PEX. Do not store it outdoors. Each PEX pipe manufacturer publishes maximum recommended UV exposure limits. So install it and get it covered up and in the dark fast. Don't wait around.
Chlorine/chloramines destroys PEX. Municipalities use free chlorine to disinfect the water supply system. If the water that enters the house has a disinfectant level of less than 4.0 parts per million (ppm), the pipe may have a long life. How long, I don't know. Is it good enough to say that the pipe will not have to be replace after 20 years? 30 years? more? I believe I read that the PEX manufacture adds a disinfectant inhibitor to the PEX, but how long will the inhibitor last before the disinfectant starts attaching and destroying the PEX? This will probably depend on the manufacture and the quality of the product. (Can manufacture expert validate this inhibitor statement).
I don't think UV light affects copper. Chlorine/chloramines is corrosive to copper. But which is more tolerant and will have a longer life (PEX, copper). Preferable, I want the plumbing to be worry free and last until I am long dead and gone (100+ years). BTW, my kids will inherent the house.
The HUD document provide information for Joining Methods which is related to your original question.
I hope this is helpful.
