Generally speaking, Chengwu Jiang Datou Xinyu and Hong Fangyuan are both authentic. Specifically, Hongfangyuan’s sauce has a stronger flavor and is more affordable, while Xinyu Sauce’s sauce has a less intense flavor.

Some people prefer Hong Fangyuan’s Sauce Datou because it has a richer sauce flavor and is more affordable. In addition, Hong Fangyuan's predecessor was the old "Xinyu", so Hong Fangyuan's Jiang Datou can also be considered an improved version of Xinyu Jiang Datou. However, some people think that Xinyujiang Datou is also authentic, because Xinyu has changed his name to Hongfangyuan.

To sum up, Chengwu Sauce Datou Xinyu and Hongfangyuan are both authentic, and the specific choice depends on personal taste and needs.