There is nothing BAD about Valvoline synthetic. I have heard recently that they like Castrol, Pennzoil and virtually all of the remaining commercial US bottlers are using a class III hydroisomerized base stock vs. the PAO of Amsoil and Mobil-1. This is not that big of a deal though and it is argued that a properly additivized class III can be just as good if not better than a mediaocre class IV.
So don't worry about it. If you want the best, buy Amsoil and feel free to contact me via e-mail with questions as to why it is the best.