The distinction is between Dolby Vision and HDR10, as both are HDR formats that Apple TV 4K supports.
Dolby Vision HDR: everything you need to know - Whathifi.com
Dolby Vision takes the dynamic range enhancements to a higher level over HDR10. When supported, DV should give a better picture.
In my opinion, most important is to set your Apple TV to match the output to the dynamic range of the source. Then SDR stays SDR, HDR10 stays HDR10 and Dolby Vision stays Dolby Vision, as the makers intended, without artificial conversions.
I see no reason to choose HDR10 over DV, when both are available.
That being said, the results may vary by title. Some movies really take advantage of the format, while others are less impressive.