This is quite a hard one, undoubtedly there were films that I fell in love with at the time, Bonnie and Clyde springs to mind, it was my first sneaky "X" rated film, I think I was 15 at the time, but not sure I'd put that on my list now. Same with Saturday Night Fever, loved it at the time. And depending on mood, feel good films that present the romanticised Hollywood version of chocolate box England, Bridget Jones Love Actually spring to mind. However, those below would be my definitive all time favourites.
Godfather 1 and 2
Barry Lyndon
Doctor Zhivago
Ryan's Daughter
Sound of Music
Gone With The Wind
Gladiator
The English Patient
Butch Cassidy and The Sundance Kid
Hook