This note is outdated, I have since switched to Emacs Plus with Homebrew. See here: Install Emacs on the Mac - Part Two.
There are many ways to install Emacs on the Mac, from pre-build Applications, to Homebrew, to installing from source.
My current favorite way to get the latest Emacs which has some additional stuff for the Mac is by using a build script, which builds Emacs from its source.
It’s called build-emacs-macos and is on Github. The instructions to use it are here in the README.