It's Rock and Roll Baby

What musical groups have sold the most records in the world?

In  rank order, they are:

1. The Beatles — 183 million units
2. Garth Brooks — 156 million units
3. Elvis Presley — 146.5 million units
4. Eagles — 120 million units
5. Led Zeppelin — 111.5 million units
6. Billy Joel — 84.5 million units
7. Michael Jackson — 84 million units
8. Elton John — 79 million units
9. AC/DC — 75 million units
10. Pink Floyd — 75 million units

Of course, this list does not take into consideration the new 

musical wonder group from South Korea:  

                                BTS...  (Korean: 방탄소년단; RR: Bangtan Sonyeondan), also known as the Bangtan Boys, is a seven-member South Korean boy band that began formation in 2010 and debuted in 2013 under Big Hit Entertainment.[3] The septet—composed of RM, Jin, Suga, J-Hope, Jimin, V, and Jungkook—co-writes and co-produces much of their own output. Originally a hip hop group, their musical style has evolved to include a wide range of genres. Their lyrics, often focused on personal and social commentary, touch on the themes of mental health, troubles of school-age youth, loss, the journey towards loving oneself, and individualism. Their work features references to literature and psychological concepts and includes an alternative universe storyline. The group has released several albums and performed on several world tours.

HOWEVER,

Bing Crosby's 1942 WHITE CHRISTMAS has sold the most single copies worldwide in musical history...  odd, since the song is about a Christian Holiday and no doubt there are many non Christians who celebrate Christmas because it is the day that presents are exchanged and lots of food is eaten and lots of alcohol is consumed regardless of the religious underpinnings.