Haven’t had a samsung phone since the note 3, but I remember having issues with unlocking the bootloader, I think you had to use some 3rd party tool because samsung provided no guide in their manual. With nexus and pixel phones it’s really easy so them I can definately recommend.
According to wireguard itself the kernel-module based backend is more efficient/faster than the userspace implementation, and to use that it still requires root.
With LineageOS + microg I have a cheap phone that performs really well and the battery lasts for multiple days. Had a jailbroken iphone before switching to Android but have never even thougt about going back.
Haven’t had a samsung phone since the note 3, but I remember having issues with unlocking the bootloader, I think you had to use some 3rd party tool because samsung provided no guide in their manual. With nexus and pixel phones it’s really easy so them I can definately recommend.