In terms of privacy, Android is "compromised" by default, i.e. Google collects and stores a ton of private information about you. I believe Apple used to be much better, and still is, but getting worse.
However, this is a speculation, so please take it as a grain of salt.
Apple also does the same. Also, this only applies if you're running an Android device "out-of-the-box". Fortunately, there exist AOSP forks that mitigate this type of intrusion (e.g. GrapheneOS).
Either the sandbox is very weak and Apple instead relies on App Store audits, or they disallow users installing apps outside the app store to protect their 30% tax that makes them a LOT of money.
The pKVM hypervisor is new to Android 13 and Pixel 7, which are a few months old.
I would also assume the fact that their vertical integration all the way down to silicon is an advantage here as well.
With the exception of the blobs, everything on Android is auditable.
Meanwhile very little of MacOS or iOS is auditable.
Personally I do not use or trust any of the above, but if forced to choose Android is worlds ahead of iOS in terms of publicly auditable privacy and security.
You cannot form reasonable confidence something is secure unless it can be readily audited by yourself or capable unbiased third parties of your choosing. This means source code availability is a hard requirement for any security claims. Even if you had teams de-compile everything you could never keep up with updates.
Not all open source code is secure, but all secure code is open source.
The bug bounty is pretty hard to actually get access to, there’s still no source outside of the kernel, and the Security Research Devices are really hard to get access to. You have to be someone they’ve heard of, in a country they approve of, you can’t move the device around, and you have to sign your life away to get it for 12* months.
I suspect remarkably few people are qualified to objectively say which is more secure. If you're an expert on one, you're unlikely to be an expert on the other.
Security is multidimensional. It's unlikely there will be a platform that's more secure from every possible angle. What's secure for you might not be secure for a less technical person, or a world traveler.
Noob here, I recall often hearing that iOS has superior security to Android. Has this situation reversed in the last few years, or was it never true?