* Alexa (in my kitchen) almost always plays the music I ask for on Spotify. Siri (in my car) gets it wrong about half the time — often in comical and bizarre ways.
* Siri remains unable to call one of my family contacts: every time, she gets into a loop asking for clarification between two options (when I clarify, she just asks again).
* I set up an automation with Siri to start the radio playing on BBC Sounds (to stop me falling back to sleep when my alarm goes in the morning). This was stupidly fiddly to set up, and it just doesn't work: Siri tells me to unlock the phone first, which destroys the whole point.
I guess the caveat is that my experience with Siri is a bit limited, because in the light of her uselessness I often don't even try to get her to do things.
Asking Siri to turn on the lights in the kitchen: “Here is what I found in the web for ‘Turn on the lights in the kitchen’”
Asking a second time: “Ok, all the lights in the kitchen are on.”
Considering how many years it's been around, these sorts of inexplicable failures are really inexcusable. Sure, I understand nobody tests their software anymore, but "predictable" is not the term I would use to describe Siri.
Apple has been consistent in signaling that they want to push as much AI to the device as they can, for example on-device speech recognition was a heavily promoted milestone. That approach is broadly incompatible with using one enormous cloud model to provide rich interactions.
I think the goal for Siri is to become a better and better decision tree, rather than a conversation-driven knowledge engine like Google and Amazon have. I support that, I have actual humans to talk to and like that my interactions with Siri are based on simple phrases which do something and don't bottom out in a Google search or (yuck) a pitch to buy some service.
Addendum: Siri does bottom out on a search of the web, yes, what I mean is that Siri encourages use patterns (at least for me) where this basically never happens.