Hello Liu Honggui. According to the query calligraphy website:
1. Rank: Liu Honggui was Wu Zetian’s imperial calligrapher, Cheng Daibin was a copyist, and Liu Honggui’s rank was higher than that of Cheng Daibin.
2. Works: Liu Honggui's "Diamond Sutra" is known as the best small regular script in the Tang Dynasty, and his works are better than Cheng Daibin's "Diamond Sutra".