Mac has major package management issues. Homebrew is fine (not as good as the linux counterparts, but fine), but if you make the mistake of installing Ruby with RVM Homebrew won't work, and you will spend a lot of time fixing it. With Arch you just have to get your basics set up and any development related item you need, there are precompiled packages you will install in seconds.
Perhaps, my point was that if you screw up your Ruby installation on Mac it is a pain to get things right again. RVM is the recommended way to install Ruby according to ruby-lang.org.
Homebrew expects ruby to be installed at /usr/bin. RVM installs it in ~/.rvm/bin/ruby-$VERSION. Even if you symlink there are compatibility problems. I'm sure it's fixable, but non-trivially so.
