Not quite certain what you meant by Post Humans, but of the races presented I voted for Elans.
The Azurin seem to lack depth, and they come across as more of a plot device for the book in which they were presented than an actual entity. (ie: There must be three new races for the book, but we're out of ideas. So we'll use bluish humanoids with an affinity for the powers represented in the book.) I think a better job could have been done if they had given the idea of incarnum more thought and consideration (as to its affects upon a society's form and structure when it is plentiful and often and openly used, etc).
The Illumians come across only slightly better. Their humans with rune-shaped insubstancial ioun 'stones' circling them. Since I never use or allow Ioun stones in my campaign worlds (even when using worlds where such are supposed to exist) I was already a little against their concept. Now, I am willing to consider thier use in my campaigns, but the runes are marks akin to Dragonmarks (as seen in Eberron). After this I can almost get my mind around them, but it still comes across to me as a con on the part of the ones granting the marks (and perhaps the ability to create similar marks later in experience). They state they have transcended their humanity and show they have a few marks as proof - magical tattoos that grant often minor supernatural abilities. Those that they convince to join their view of things may also eventually learn the 'rituals' for creating such marks upon themselves. No, that could be an interesting plot hook for an NPC known to the PCs, but it does not come across as a realistic 'other' race - more a culture devoted to the concept of magical tattooing.
Elans, however, come across as distinctly different. They awaken to find themselves fully grown, discovering that they were in fact priorly another individual with a full lifetime of experiences, talents, and skills, but such has been washed away by willing symbiosis with a greater intellect than their own - the synthesis of which now wears their body like comfortable and familiar clothing. They are remade and lack anything resembling a childhood (as such is completely lost to them). They might later come upon those that knew their prior self, but to him they are complete and utter strangers, and the one they speak of may have little in common with the 'man' the synthesis has become (if such could even truly be called a 'man'). More interestingly yet, they are classified as Aberrations due to the fact that they are in truth a symthesis organism - human flesh encasing not a human soul but instead a psychic spirit entity - that perhaps is enmeshed, fused, or otherwise in combination with the prior soul.
This presumes, of course, that the entire thing is not a sham to slowly replace humans with Quori spirits wearing human flesh - akin to bodysnatcher style stories. Even if the latter is true, the whole situation has more depth, convolutions, and potential for intrigue (and intriguing) adventures than the prior two - which only seem to attempt for such without quite managing it.
My only qualm with the race is that it should be a template applicable to any humanoid, as only the mind / spirit alters. Furthermore, as their flesh is not aberrant they should still count as Humanoid for the purpose of traits that affect the physical body (Str, Dex, Con, Petrification, Nausia, Alter Self, Polymorph, etc), while counting as Aberrations for the purpose of traits that affect the mind / soul (Int, Wis, Cha, Fear, Charm Person, Mind Jar, etc). And, as a partial Aberration, they should be allowed Aberrant Feats (which they are).
It would have been interesting to see this as a template, seeing it applied to half-elves, gnomes, elves, etc. Of course, they would need better definitions as to what is lost upon applying the template (racial vs cultural traits). Right now all would be lost (according to the FAQ), but that's just plain nonsensical and should be ignored.