I use a lot of different music. In order to help you in the way that matters most to you, what kind of device are you using to play the music (CD player, iPod, other) and are you interested in purchasing individual songs, hour-long mixes, or would you consider using a service like Spotify or Apple Music that allows you to stream music?
I used iTunes to purchase individual songs and upload purchased CDs of hour-long mixes for about 6 years. I just got a subscription to Spotify Premium, so I’m learning the ropes of making playlists and finding music, but I LOVE that I can update my music with every class and not have to buy one song at a time.
My HIIT classes are mainly clients aged 30-50, so we use a lot of classic rock.