Gian Lorenzo Bernini's Apollo and Daphne is my favorite Hellenistic sculpture. The detail all the way down to her fingers becoming branches is amazing. Her flesh looks soft and malleable, even though it is carved from hard marble. The skill and work that went into this piece blows my mind!
As for classical... I'd say the Three Graces marble sculpture by Antonio Canova. The women have such kind, loving looks about them. Both on their faces and through their poses. Though the figures are more ridged than that of the Hellenistic period, they still show the classical ideal of perfection.
