There has been a lot of research on this if anyone has an AES membership thye cans view people preferences. Harman does make much of their research available online on their website. In a nutshell people without hearing problems prefer a flat sound with a natural slight roll off of highs common with sitting a little distance away greater than 10ft. At lower volumes more bass is desired as our hearing is less sensitive to hearing at lower volumes. Hence the old "loudness" button. Bass counts for about 30% of subjective ratings but it is not just quantity but quality like tight not boomy, etc.

Flat speakers tend to sound better and less fatiguing over time. If you are trying to sell speakers the happy face curve can add bass and sparkle to the highs which immediately gets someone's attention but is often fatiguing when listening for longer periods of time. This is what a lot of research has shown.

Of course people with hearing loss will boost the frequencies they are deficient. As we get older many people suffer from high frequency hearing loss and the happy face highs they will often like.