Is Ujjain or Trimbakeshwar better for the puja?

Both are powerful locations. Trimbakeshwar is widely regarded as the single most potent location because its Jyotirlinga bears the three-faced aspect of Brahma, Vishnu, and Shiva, and the ceremony there can be combined with Pind Daan to address the ancestral karmic component simultaneously. Ujjain is preferred when the dosha has a strong Mars connection, given Ujjain Mangalnath Temple is the mythological birthplace of Mars.