I'd argue all of them. Any true exponential eventually gets to a point where no computer can even store its numerical value. It's a physically absurd curve.
If we suppose this tech rapture does happen, all bets are off; in that sense it's probably better to assume the curve is sigmoidal, since the alternative is literally beyond human comprehension.
At the stage of development we are today, no one cares how fast it takes for the exponent to go from eating our galaxy to eating the whole universe, or whether it'll break some energy density constraint before it and leave a gaping zero-point energy hole where our local cluster used to be.
It'll stop eventually. What we care about is whether it stops before it breaks everything for us, here on Earth. And that's not at all a given. Fundamental limits are irrelevant to us - it's like worrying that putting too many socks in a drawer will eventually make them collapse into a black hole. The limits that are relevant to us are much lower, set by technological, social and economic factors. It's much harder to say where those limits lay.
My experience is that "AI can write programs" is only true for the smallest tasks, and anything slightly nontrivial will leave it incapable of even getting started. It doesn't "often makes mistakes or goes in a wrong direction". I've never seen it go anywhere near the right direction for a nontrivial task.
That doesn't mean it won't have a large impact; as an autocomplete these things can be quite useful today. But when we have a more honest look at what it can do now, it's less obvious that we'll hit some kind of singularity before hitting a constraint.