My favourite part was All Might's fight against AfO. I was genuinely worried he'd die. Great decision on Horikoshi's part to keep him alive after that. Otherwise I enjoyed almost everything focusing on the class, be it the tournament, training sessions, fighting against class B, exams or the festival.
And Twice. Everything about Twice was amazing.
First big dud was definitely Overhaul's arc. Miro and Eri were great, honestly Overhaul was pretty fun as well. But that's when we started shifting focus to the older heroes, action scenes became hard to follow and it felt less about the character's personal developments and more like brainless action. There's still moments I enjoy, especially visually, so long as it's not a big fight Horikoshi is an insanely talented artist, and I like the direction he takes the story in. I just wish we'd kept focusing on the class and not New Character #45. All this big scale country saving action is cool, but it's when he keeps it focused on the everyday people that it shines.