From a subjective perspective? 2-1 is my favorite. It's not the best writing-wise. but It's a fun trial with a very good and fun mystery to solve, every character felt involved in some way (surprising for a first trial ) , and the interactions were great. It introduces us to new trial minigames like rebuttal showdown and the new hangman gambit ( Which is my favorite of them all, I know I'm a masochist ) And it introduces us to the "antagonist" of the games, I love how they handled the Nagito plot twist, the reveal felt impactful and quite shocking, it also did a great job to introduced him and the threat that he will be, but also how complex and crazy he is. I could go into more detail about every reason why I love this trial, but it would take too much time and frankly I need to sleep. But yeah, It was the trial I had the most fun with and also the one I like to replay the most.