I am of the opinion that nothing beats our own imagination
The only reason I can think of for people using AI as a companion is that, unlike our imagination, the responses are not known beforehand with AI, but in my imagination my waifu can punch an evil robot so hard that the force of the punch pushes into a skyscraper from which she jumps off while spinning 32 times and softly landing in front of me and then I'd clap and raise a sign that says "10" and she would be very flustered and cute
AI could do that too but I assume it would need a fair bit of coaching