I quite like the relativenumber option (paired with the number option), because I'm terrible at being able to use numbered motions without it.
I'm not sure what my favorite plugin would be (so many to choose from!), but my favorite Neovim color scheme has been "GitHub Dark Tritanopia" from the github-nvim-theme package.
Oh, and for another favorite tweak of mine, I always have vnoremap $ g_ set so that using $ doesn't copy the new line character.
Pretty basic, but I like setting backupdir and directory so I don't have to add vim undo and swap files to my .gitignore. Also, noerrorbells because sounds irritate me and I frequently intentionally do things that would trigger them.