Always autonomy on. If there was no autonomy I wouldn't even play this game.
I love to watch the Sims on their own, what they choose to do, it often brings out interesting personalities. They have their favorite things they love to do and even with Sims that have the same traits and aspiration the interests and/or obsessions seem different. My Sim had identical twins with same aspiration and traits and they had completely different interests.
Quite often I just let my Sims do whatever they want, I don't need to control them all the time, unless I need to grind skills or aspiration completion.
I also like to see if my Sim wants to flirt with someone, either autonomously or if there's a whim. One of my Sim had a whim to flirt with Travis Scott after he came to visit her with the "welcome wagon". They ended up married later, because that was also her whim.