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.
Creating playlists used to be time consuming until I was introduced to Spotify by my daughter. Spotify is really great for customizing workout music. Now I ask for any special music requests and can add them to the playlist immediately. This worked great for adding and deleting special occasion and holiday music.
I also teach a HIIT class and use current music playlists for this class. I still like to order my music online with playlists already created. You may want to experiment with different types of music as sometimes it also depends on the time of day. (for example, some of my classes are at 5:45 in the morning, and hard rock is a bit too much for that group).
While I don’t necessarily need to “go to the beat” during my class, I prefer a pre-made mix with a constant beat and no rest between songs to keep the flow moving.
Hope some of these suggestions help you.