It's very difficult to choose one. So I'd go with "Yeh Jawaani Hai Deewani" & "Zindagi Na Milegi Dobaara".
ZNMD, YJHD, Dil chahta hai
Yeh jawani hai deewani ..always !
I would have to say 3 idiots and jaane tu ya jaane na
Zindagi na milegi dobara is totally relatable to friendship.
My all time favourite is yeh Jawaani hai deewani