The Shimano RD is moving more because there is a spring pivot on the RD mounting bolt, that's why it is bouncing more. The SRAM RD doesn't have a pivot on the mounting bolt, rather, it is rigidly fixed to the gear hanger.
When shifting on flat ground, both should work equally well. But when shifting on bumpy terrain, the Shimano RD might be bouncing too much to shift accurately.
However, the pivot on the Shimano RD can be thought of as a "suspension" for the RD. It absorbs the movement of the RD when over bumpy terrain, reducing risk of damage to RD or gear hanger. Also, if you accidentally bump your Shimano RD against a rock or something, the pivot might help to absorb the impact and prevent damage.