Which is the most authentic Old Beijing Shabu Shabu?

I think Nanmen Shabu Shabu is the most authentic of the Old Beijing Shabu Shabu.

Since its founding in 1994, Nanmen Shabu Shabu has won high recognition in the capital and among the general public for its honesty and unique recipes. One of Nanmen Shabu Shabu's specialties is the freshly cut lamb tendon, and the shabu shabu melon strips are also a well-received dish.

Beijing's traditional halal shabu-shabu was first called "Hongyuan Shabu-shabu", but is often referred to as "Nanmen Shabu-shabu" by customers and friends because the main restaurant is located at the south gate of Tiantan Park in the South Second Ring Road.