There's no way I could ever pick a favorite. But right now I've been in love with Camille Saint-Saƫns' "Air Et danse-Bacchanale" from Samson and Delilah.
...but I think I must have been changed several times since then.
The "Agnus Dei" movement from John Rutter's Requiem is my all time favorite. But I like most of the music of the late classical period and romantic period.
I could never pick a favorite piece but currently I'm playing Debussy's piano prelude The Girl With The Flaxen Hair. It's gorgeous! I love playing it, good for getting feelings out.
I have this strange passion for the 1st movement of Telemann's 4th Methodical Sonata for flute in E major ... but I can't actually choose one. I'd say that I love pratically all the compositions of the Baroque Era ~