You’re looking for “Immersion” by Aliette de Bodard.

1. Publication data
   • First published in Clarkesworld Magazine #69, June 2012
   • Reprinted in several “Year’s Best” anthologies
   • Winner of the 2013 Nebula Award for Best Short Story, finalist for the Hugo and the Locus Awards

2. Why it matches the description

   • Social split: the story contrasts the “Galactics”, the interstellar élite who rely on extremely sophisticated wearable/implanted expert-systems called immersers, with the poor “station” inhabitants sometimes derisively nick-named “hive-rats”.
   • The immerser: a circlet of nanotech and projected light that constantly adjusts the wearer’s face, posture, voice, word-choice and even emotional affect so that whoever is looking at her sees – and hears – exactly what will please them most.
   • Malfunction and repair: the plot starts when a Galactic noblewoman whose immerser is beginning to glitch is taken by her companion (in the OP’s memory, a “father”) into the poorer levels of Longevity Station to find someone who can fix it. The repair shop/restaurant is run by a local family; the narrator is the shop-keeper’s daughter Quy.
   • Looking behind the veil: Quy becomes fascinated by the noblewoman, tries to peer past the projections, and discovers that because the woman has worn an immerser since early childhood – “before ego formation”, as the OP phrases it – there’s almost no personality left inside the hardware shell. The same is true of her male companion and, by implication, most upper-class Galactics.
   • “The AIs are more the person than anything”: that sentence is almost a direct paraphrase of de Bodard’s description – the immerser makes every decision, the wearer merely supplies the biological substrate.
   • Awards: the comment the OP saw remembered it (correctly) as a Nebula winner.

3. Short synopsis

Quy, a teenage girl who helps in her family’s waterfront café–repair shop on Longevity Station, watches two impeccably beautiful Galactic visitors: a man and his “cousin” Lê Thi Linh, whose immerser is beginning to slip. While Quy’s brother tries to repair the device, Quy realises that Linh is almost catatonic without its prompts. The immerser’s seductive promise of effortless acceptance has hollowed its wearer out. Quy must decide whether to give the device back, condemning Linh to continued erasure, or to break it and let the woman rediscover what little self remains. In the end she smashes the machine, an act that may spark wider resistance among both stationers and Galactics who have begun to suspect that the technology that makes them “perfect” is also destroying them.

That mixture of under-city “hive-rats”, nobility whose every word and gesture is scripted by AI “appearance/voice/stim” tech, and the revelation that the real human inside has regressed to an infant-like state, is exactly the story you’re remembering.