A convincing conversation partner is mostly a matter of restraint. Too eager and it reads as a script; too distant and there is nothing to hold. The cast on Yourmove AI is tuned between those two extremes.
Voice before features
Each companion has a vocabulary, a rhythm and a few blind spots. Those constraints are what make a character recognisable after a few minutes of talk.
Continuity
Returning to the same partner builds shorthand. Jokes recur, plans get referenced, and the exchange starts to feel earned.
Choosing one
Read two or three profiles and pick the voice you would actually want in the room. That instinct is usually right.