Previously this would be OnePlus, but it looks like their newest phones aren’t rootable. I used to have a Xiaomi phone for this also, are they still good?
Ik you can root smartphones from a lot of brands but I’m looking for one that has good ROM support and doesn’t try all kinds of tricks / to prevent you from unlocking the bootloader
Google but buy directly from them and not carrier, used market on eBay is good but make sure you get factory unlocked