Git is nicer to use than SVN (in my opinion) but SVN is better for the WordPress repo (sadly). SVN doesn't keep every commit like Git and therefore you get a "snapshot of the plugin" at the appropriate states. Has anyone ever tried to just download WordPress version 4.1.1 from Github? You endup with 100+mb because you're getting EVERY version and little change.

Point is that like it or not your going to have to use both if you plan on uploading your plugin to WordPress.org. Your plugin will be removed if Otto catches people simply pushing up their entire git repo of their plugin to the WordPress plugin repo.

Also, if your using git as your main source control your plugin will be near impossible to find. Github and other git based repos are just not easily searchable for WordPress plugins.