This aria – “Behind Those Soft Curtains” – is from the opera “Manon Lescaut” (1893), Puccini‘s third opera and his first great success.
Finding “the best” key for this aria is not an easy choice. In the Ricordi/Hal Leonard edition (with play-along piano accompaniment CD) the aria has been transposed to a key one tone higher (F) than in the original vocal version (Eb). Both versions are offered here.
F major: Clean Performance Version  F major: Edited Performance Version      Piano Score
Eb major: Clean Performance Version  Eb major: Edited Performance Version    Piano Score