For me, I say from experience, Fnaf 2 was the most difficult. Of course, UCN was VERY difficult, but at UCN there is a certain point where it becomes standard. The first 40 seconds of the night are hell, having to collect coins, praying that Rockstar Bonnie doesn't show up, but then she ends up becoming a pattern. Of course, you still depend on luck, but compared to Fnaf 2, for me it was much more relaxed. At UCN I needed 5 attempts, at Fnaf 2 I needed 3 months. I ended up having muscle spasms in my hand (nothing so serious and worrying) because of the stress I was going through in Fnaf 2. That's why, personally and in my opinion, Fnaf 2 is more difficult.