OK, OK! Speakers are best.
In a lot of ways.
But not in a lot of circumstances.
--Not if they are quite inexpensive (specifically as inexpensive as many of the most-respected headphones).
--Not if they are not meticulously placed.
--Not if the listener is not meticulously placed.
--Not if they are run only so quietly as to disturb no one.
--Not if the room or speaker is not treated to reduce room effects.
If any of those conditions are not met, chances are that a headphone will outperform the speakers.
What this all adds up to is that speakers are better than headphones but still far from ideal. Moreover, headphones present music in a peculiar way that differs--maybe valuably--from the presentation of the same music through speakers.
Headphones are superior to speakers certainly in the detail of the presentation and offer a soundstage that is, let's just say very attention-getting. Not realistic because speakers come much closer to that with most recordings which are aimed at speaker reproduction, but maybe the headphone soundstage is valuable in keeping the listener involved with the music.
So, I think it is possible to prefer the headphone experience to the speaker one. It's not compulsory to prefer either, and being AC/DC is probably ideal.
Both headphone and speaker reproduction are extremely unrealistic by comparison with live originals (in the kinds of music where that applies). If realism were the only criterion for our music reproduction, then binaural recordings through headphones might be the best choice and by a broad margin. But those recordings almost don't exist. There is simply too little such material to make that a serious option.
And, then, too...is realism what we really want? Don't we really crave something as exciting as our best live music experiences? Would we like binaural realism if we heard it? Or would it seem flat, distant, inconsequential.
That we really don't want mere realism in our reproduced sound is maybe most strongly indicated by the almost universal use of Foley artists to punch up movie soundtracks. Don't we want to somehow "break through" the recording process to get at the music? Or am I being a mystical sort of heretic?