AirTags only come in a single size and shape that only makes sense for larger container objects. Tile makes a flat credit-card sized variant that you can slide in your wallet, and the adapters required to put an AirTag on a keychain is pretty ridiculous in comparison to the tiny variants you can get from Tile with a built-in hole for this purpose.
(Also: AFAIK the "large"--not really, in comparison to the AirTag + adapter, lol--Tile Pro variants have a noticeably longer range than AirTags.) Honestly, the only thing, to me, missing from Tile is the direction arrow finder, which is certainly useful, and yet... the speakers on the Tile are much much better so it just doesn't matter so much?
(BTW: it is extremely stupid that that arrow only works in two directions. I waste so much time following the arrow only to realize I need to go upstairs -- I live in a two story apartment with a bedroom and an office above my kitchen and living room: it isn't larger than my friends's apartments, but it is really nice having two floors -- that I am only doing because the sound isn't loud enough on AirTags.)
Frankly, the whole argument for AirTags being inherently better is merely that they have a "bigger network", but for most of my objects I am not scavenging around town looking for then, nor am I ever going to be chasing some thief around the city in my car looking to steal it back, hoping to catch up to them before they disable or throw out the tracker... that vigilante justice idea associated with this product category is just a crazy pipe dream.
Instead, I am pretty much always just trying to figure out which pair of pants I left my wallet in today, or on which shelf I left my keys: I would actually be much happier with a purely local product that only responded to encrypted pings from my personal phone and only even did that when I actively ask it to (as despite using both Tile and AirTags for years now the "you left your item behind" notifications have only happened before I myself noticed once or twice in a way which was helpful... it just doesn't ping often enough, with either product, to be maximally useful).
And looking at the replies to this, I have learned AirTags are actually missing what is to me a glorious feature of Tile: that I can push a button on my keys and find my phone in reverse. I hadn't noticed this lack before as I am only using AirTags in large objects I don't keep on my person (which makes their notifications really annoying as the UI fails to eat old ones even when I walk back to my object... this seems very fixable), but I don't want to have to buy an Apple Watch just to have a way to find my phone :/.