A couple years ago, the 5W-40 was the BC, made in Belgium, but then Castrol started to make it in the USA. Was great stuff back then, but don't know about now.
Yeah Autozone carries the 5W-40, last time I went there it was ~$6.19/quart. They might have some special deal once in a while where you get 5 quarts Castrol Syntec and a oil filter for a good price.