Wow. Walk away for a day or so, and lots of replies.
What, in your experiences, sets fae, elves, sidhe and danaan apart?
I struggled with this for a long time, partly because I think I am or have been more than one, and trying to understand what bit of me was related to what type was an ever-tangling ball of string.
I tried to look back at basics - literature, folklore, and mythology from as far back as I could find, which pretty much led back into Yeats collections of folklore, some reasonable books on Norse and Celtic mythology, and things like the Mabinogion, with side looks at the Eddas and the Kalevala.. That got more confusing, not less, as many of the terms are used pretty much interchangeably in various places at various times.
Over time, I did find enough things that seemed to fit that I started building my list of things that seemed to be more one than another, and then I added what I learned from energy work with various types, and from examining those I could.
That led pretty much to the below.
Nature: A being of Faerie
Form: Varies wildly.
Glamour that feels/sounds/sparkles like the raw energy of Faerie itself.
To me, this feels/sounds like golden notes, and sparkles clear to gold.
Nature: Sidhe (unique energetic resonances, distinct type of Glamour)
Form: Humanoid, although form varies somewhat
Sometimes from Faerie, but not exactly of Faerie - Sidhe Feel more like Underhill than like Faerie.
Glamour that feels more silver/blue, with golden sparkles.
Caveat: This gets somewhat confusing when dealing with the Danaan/Sidhe hybrids (Danaan Sidhe, Daoine Sidhe, Duena Sidhe, etc. depending on region). Some manifest both Danaan and Sidhe traits, or a blurring/blending of the two.
Nature: Altered Human
(According to the Book of Invasions, these were people who followed Danu's voice to her lands, dwelt in her presence, and were changed by that experience - and their descendents)
Glamour is more bronze/brass than gold, but there is some gold.
Glamour feels somewhat like Fae glamour, but not the same.
The Elves with whom I'm most familiar are the Elenari.
Form: In general, Elenari are physically similar to the common conception of Sidhe or of "Tolkein Elves".
For those from Sel'ar, this is more true of the Tulari, Listari, and Altari, and less true of the Draestari.
In general, Elenari don't have Faerie/Sidhe/Danaan type glamour (certainly some Shiri are an exception to this).
The thing that makes Elenari what they are is the Song that flows through them. It affects their selves, their lives, their choices.
In those who manifest Elenari strongly in this life, it still does so.
Side note, from my perceptions:
The Aloryans feel very much like a divergent blend of Tulari and Altari.
The Shiri are even more different, and feel more like Tulari or Listari blended with Sidhe.
Elenari are not a hive-mind, but in many ways they could be said to Flow Together: they tend to think of the same types of things, to make the same types of decisions, and to move in the same directions in response to situations. Elenari are somehow connected, especially those of similar cultures, and it subconsciously causes them to affect one another. Even here, reincarnated, those tendencies tend to re-assert.
I tend to think that their Song is both a cause of that, and a result.