Answer:
That would depend on if you do it or not. If you can braze/solder copper fittings, which really isnt hard to do, but if never done before, forget the copper unless you try a special type of adhesive they recently have come out with Super HVAC I think its called? They joined a 3/8 to a 3/4 to a 1/2 inch with just this stuff, and no couplers! and its strong! Unorthodox, dont know if I would gothat way over hiring a guy to run and solder the place up with my help.
PVC is legal in some areas,,not my favorite unless its accessible, same for PET or that new flex stuff thats the latest fad.