Over time two plugins were developed for Sublime Text 3. Both of them have the same aim to help with development in Flow, but they differ in the approach they take to achieve it.
The original plugin that was developed for Sublime Text 2 first, then ported to Sublime Text 3.
It may be harder to setup and tame, but brings more advanced features to the table.
The newer plugin that started as a fork with bugfixes, but has grown to have a completely different approach.
It aims to provide an out of the box package, that allows to dive into Flow in as few steps as possible.
It is easier to setup and more stable, but lacks more advanced features.