i have both so hear it goes
PVC:
cheaper ($3 per 10ft)
slides all year round without wax/water
pretty durable
the only downside is it SUPER slippery, like faster than metal, so it can be hard to learn switch ups and 270's on cause it slides so fast
Decking:
expensive
you need to keep it wet when u ski on it, this wont be a problem in the summer(hose) but in the winter if its a bone dry cold day it simply wont slide that well
decking is wider and much slower than pvc, so you will find it much easier to learn tricks on it
NOTE: if u choose decking, make sure you get the kind with grooves in it, DO NOT GET the perfectly smooth type, it wont slide for shit
good luck