There are several different ways to make synthetic oil, some better than others. I don't know what the Wal-Mart brand synthetic is based on, but I trust Mobil One. The extra few $ is inconsequential, spread over 5,000 miles.

BTW, one of the local Wal-Marts here sells quarts of Mobil One for $3.38, which actually works out cheaper than the same store's price for the 5 quart container. None of the other Wal-Marts have that low of a quart price, though. It has been that way for years for some obscure reason...I swing by there every once and a while and buy a couple of cases.