vim is often the default editor. It is surprisingly better than nano, although sometimes nano is the default (e.g. Ubuntu). One nice feature of vim is that it already contains several nice vimrc files for git (in addition to many, many code syntax files) e.g.: gitconfig.vimrc, gitcommit.vimrc, etc. But, vim's default syntax setting on mac is surprisingly off! So turn it on. But first start the mac terminal.
dude@mac ~$ echo syntax on >> ~/.vimrc
in case you already have a .vimrc file, use the double greater-than sign to append to it.
Ah, now isn't that a lot nicer?
P.S. If you dare to try nano, check out these nanorc on Github, since you won't find them on your mac. (ha!)