They are the same thing really. New aio is just the old one with a built in receiver. Which technically makes it heavier than old external version if you weigh them both out, but just barely. I’d just get whatever is in stock and is cheapest between the two. Both the air65 and the air75 were updated in this manor this year.
The new antenna design is nice though.
As far as what one to get a 75 will be flys or inside but a little harder due to more power and larger. A 65 however won’t fly outside as well. I couldn’t decide what one to get either, so I got both lol. I fly the 65 more often though, outside too for guerrilla whooping :)