How is this even a question, when we're talking about an OS designed from the ground up to shove ads in your face at every step and track your every move? I miss Nokia/Symbian so much, a powerful OS with several features still missing from Android as of the latest version, and no advertising bullshit built into it.
Today you're stuck between non stop ads and a locked down FisherPrice OS that you pay through the nose for (iOS)
Can't imagine not rooting in order to nuke all ad related components from apps, as well as being able to do a nandroid backup of all my app data. And that's before we come to awesome custom ROMs like LineageOS and its derivatives.
Easy to root and supported by popular custom ROMs is the first consideration for me when looking at new phones. Rocking a OnePlus 3 for almost 3 years now, with Resurrection Remix Pie, and all security patches for Android upto July 2019.