How do we determine who is better for leading the prayer between a bearded man who recites the Qur’an well but errs in pronouncing the letter “dhāl,” and another who recites the Qur’an fluently and has memorized some of it, but trims his beard and wears trousers and a shirt?

Trimming the beard is not permissible. Praying behind an imam who substitutes one letter for another in Al-Fatihah is not permissible according to the majority of scholars. It is more appropriate for you to lead the prayer if you can recite correctly, while being careful to wear loose clothing that does not reveal the size of the limbs.