I enjoy Lorena McKennit voice in general, it's like an angel, such a clear, sensitive, sparkling soprano. I love playing her Winter Garden album during Christmas time, it contains some beautiful traditional Christmas carols like God Rest Ye Merry Gentlemen and Good King Wenceslas.
Bryn Terfel has a nice Christmas album too. I also like to hear Judy Garland sing Have Yourself a Merry Little Christmas from the classic movie Meet Me in St Louis.
My favorite Christmas Song is O Holy Night though. It's hard to pick a favorite cover because there are so many good ones. Maybe Josh Groban's version. He has such a golden, warm singing voice? I want to cry when he sings the phrase, Christ is the Lord. I got chills listening to it today