Which is a better phone and why?
There is no objective answer to that. Maybe tell us your needs, use case.
Both of them aren’t good enough for privacy use cases. Using something like Universal Android Debloater is recommended.
If possible, buy a used device on which you can install official LineageOS.
Lineage OS has too many bugs when I researched it
I’ve been using LineageOS for a couple of years on a Xiaomi Mix 2. I once had a playback error with Deezer (French Spotify competition), which was fixed rather quickly. The team was reactive and had great communication about it. There are regular updates and everything works great. I psyched that my phone now has Android 14 and not 9, which is what Xiaomi left me at…
I’ve used it on a Redmi Note 8 for 2 years, and am using it on a Samsung Tablet. I never had any issue.