"better" Can be determined upon a few factors, what else is on the car and what are the driver's personal preferences.
The largest advantage of the Progress rear sway bar vs the Whiteline is three-way vs two-way adjust-ability and a larger/thicker bar. 18mm Whiteline vs 22mm Progress. Also, Whiteline uses poly bushings when Progress skips that and goes right to good old heim joints.
More options and larger roll stiffness can help or hurt depending upon the first part of this post.
The largest advantage of the Progress rear sway bar vs the Whiteline is three-way vs two-way adjust-ability and a larger/thicker bar. 18mm Whiteline vs 22mm Progress. Also, Whiteline uses poly bushings when Progress skips that and goes right to good old heim joints.
More options and larger roll stiffness can help or hurt depending upon the first part of this post.