Top 3 films?
It Started with Eve (1941)
One Hundred Men and a Girl (1937)
Three Smart Girls Grow Up (1939)
Hard to say. The three you've chosen are definitely among her best. I think of her early "child star" films, Three Smart Girls Grow Up, though a sequel, has one of the best scripts of a Durbin film, and shows her talent as a singer and an actress at its' best.
I think many film historians like First Love (1939) a lot. I do too, except that I like to see Deanna taking charge rather than being put upon by other characters in the cast.
Christmas Holiday (1944) and Lady on a Train (1945), are uncharacteristic Durbin films, and good showcases for her dramatic (Christmas Holiday) and comedic (Lady on a Train) talents in the film noir genre.