For the most Christmas Albums sold, I would have to go with the Collectibles, The Ultimate Christmas Volumes 1 through 7.
This album is marketed across the United States under popular regional Radio Station Call Letters.
On the east coast, it's called The WCBS FM Ultimate Christmas Album.
This collection of both traditional and rock'n'roll Christmas music is a treasury that will foot the bill for any corporate Christmas part all be itself!
It is a great seller, both in record shopsand on-line, and is usually hard to find.
This year they added Volume #7
The series started in 1998.