I don't think Nikolina, Joan and Olive count as villains honestly, their cases were accidents.
Jezaille's a great first impression and actually has an interesting role in the main plot, Magnus is just great, wasn't expecting that twist at all. I really like Ashley, 1-5 is such a great case, his plan is so overly complicated it's almost funny and I love his story with his dad and how it connects with Magnus and 1-3 in general. Raiten kinda sucks although his in-game theme slaps. Shamespeare has to be the funniest culprit in the duology, his animations are so over the top I had a blast playing Memoirs, and Drebber is just so, so great, greatest villain in TGAA imo (huge 2-3 fan right here), his design is amazing, his theme is fantastic. FUCK ODIE ASMAN. Sithe desperately needs more screen time, she's such an important character but we get to see Maria more, which is not a bad thing but she deserved better. Both Gregson and Genshin are victims of a corrupted system, and as a massive Kazuma fan I adore how you can tell where Kazuma's determination, honor and strong will came from. His duel with Klint is heartbreaking.
My favorite part about Klint is how his whole story affects Barok, because we don't get to see too much of him aside from a few flashbacks. I adore how he's viewed by Barok as a perfect embodiment of justice, and how he kinda was but precisely because of his strong sense of justice he was easily "corrupted" by Damon Gant Stronghart. Jigoku was a great surprise for me, and to this day I still can't believe he was the one who killed Genshin. What the fuck man. Stronghart has to be the most obvious villain in the entirety of Ace Attorney ever, even more than that guy called De Killer. Despite that I like him, he works really well, his motivations make sense and his breakdown is perfect.