Year 11 by far. It was the one year where I didn't feel like a complete socially inept mess. Our whole year group seemed to become a lot more friendly with each other too, so there was like no animosity between anyone, which was really nice. Study leave was amazing too. I had so much fun.
Year 12 has already surpassed Year 11 though in it's greatness. I've made so many more friends and the whole change you get with the teachers/school from entering sixth form has made it amazing too. So the current year I'm in is my favourite really.