Quite frankly, all of them, as in literally all of the levels. e.g., viruses are not considered "alive" in the classic sense, but they sense things sometimes & change their behavior accordingly. A single protein can do it too, like in mad cow disease / scrappy (called "prions"). Even a tiny snippet of DNA can make logical circuits akin to computer ones, implementing AND, OR, XOR, NOR, operations etc., plus feed-forward loops (& feed-backwards, and all other sorts).
Possibly even subatomic particles, and maybe even quarks (or strings?) do the same - e.g. the Heisenberg Uncertainty Principle where you start to interact with something and then that changes it already so that you cannot measure other aspects of its previous "natural state". Okay that's not so much a "decision" as a "reaction" - but as you are questioning, what really distinguishes the two, REALLY?
Bacteria can sense a molecule (like sugar), literally start growing a tail (no joke!), and then swim towards it. All entirely chemically, and we have the technology to literally just kinda 3-D print all that at the molecular level (it takes an existing flagellum but once that is added to the mix, it can grow just like a crystal, by extension / copying of the old pattern).
Most of what we considered to have made humans "special" in the word turned out to be false - e.g. chimps & gorillas can "talk" (it's hard for their throats to make our kinds of sounds, but given the right apparatus they can get the job done), and think in abstract terms, and do math, and all kinds of things. Of course, humans ARE special - we are the only things on planet earth that if aliens came, could attempt to nuke them in orbit, and we literally light up the night sky! But there's a whole continuum of "dust" that share a lot of properties with us, in various ways. I'm not sure if animals have the same kind of subconscious vs. conscious interplay going on as we do, but if you have a pet and stare at it trying to work through a decision, you KNOW that it's doing the same as us, at a fundamental level. And then each time you go a level deeper, the similarities kinda never end...
Such questions may never even find answers, at least in our lifetimes, but it sure does seem worthwhile to ask anyway... it sharpens us, so keep digging!:-)