Motion/force transmissibility is an essential property reflecting the kinematic performance of parallel robots. Research on this performance of the single-platform parallel robots has long been concerned and studied. In contrast, although many innovations and applications of the high-speed articulated-platform parallel robots have been presented, few studies on their motion/force transmissibility have been reported. This paper deals with the motion/force transmissibility analysis and comparison of two typical high-speed parallel robots with articulated platforms. A modified output transmission index for the high-speed parallel robots with articulated platforms is proposed based on a newly defined concept of equivalent transmission wrench screw. Furthermore, by having an insight into the instantaneous relative motion inside the mobile platform, a medial transmission index is proposed to evaluate its internal motion/force transmissibility. Based on these foundations, the local transmission index is redefined as the minimum value of the input, modified output, and medial transmission indices. Under the framework of above performance indices, analysis and comparison of three typical high-speed articulated-platform parallel robots, i.e., Par4, and Heli4, are presented. The results show that motion/force transmissibility of the Heli4 is better than the Par4. Inspired by the comparison, a novel TH-SR4 parallel robot with double-platform structure is developed for high-speed pick-and-place operations.