Well, the battery on my Nexus 5X is so worn out that it only lasts about two hours. I'm looking to get a new phone (I.E. no battery wear) which has similar features with regards to having an unlockable bootloader and 3rd party firmware. I'm also very open to the idea of something running an alternate OS entirely (like PureOS, but the Librem 5 is too expensive).
Just wanted to hear your thoughts and suggestions.
LineageOS is probably the most popular among them, but I have also used CopperheadOS and Sailfish. IIRC there was some controversy surrounding Copperhead though. LineageOS is a descendant of the defunct CyanogenMod.