Unfortunately, all my favorite moments are somewhat limited only having played through 2 and a half games starting with 4 and moving backward XD
4: 3 way tie, between Rika on her roller coaster crash scene, the musk cats cave, long winded cats that give you a tusk and tell you to go away XD, and the Hunters Guild, especially the mission where you have to go save Mile from the sandworm and they end up dieing anyway. lol
3: At the end in Lashute, from the start everyone is cheery and welcoming then you come in and first person says, "Your death awaits you in the city of Lashute!" XD
2: Seeing as how I'm not even really half way through, I'd have to say where that old guy goes and blows up his daughter and kills himself too! Haven't even gotten there yet. XDDDDD
My decisions were also harder because I read every one of those Conversation within Elsydeon, if anyone has heard of those, where they have little scenes in PS heaven that are the funniest things in the whole world, so far as I know.