pvc is smooth, very fast, and will break the easiest.
metal is the heaviest, slower than PVC, but will hold up a lot longer, and you cant bend it if you have a bender... you can also weld stuff together.
my 2 cents... if it is just a little mess around on back yard rail go with PVC... if you are gonna have it every year and expand on it and have it setup big and nice... go with metal
4FRNT.
Thugged out since cub scouts.