Qualcomm Snapdragon 780G Advantages
More modern manufacturing process (5nm vs 7nm)
Lower TDP (5W vs 6W)
Released 2 years and 3 months late
Qualcomm Snapdragon 855 Advantages
Better graphics card performance FLOPS (0.8985 TFLOPS vs 0.7526 TFLOPS )
Larger memory bandwidth (34.13GB/s vs 17GB/s)
Higher Frequency (2840MHz vs 2400MHz)