Core vs Reactor?

[eluser]dstegelman[/eluser]
I would go with reactor. For all purposes CI is Reactor. Its the version you would download if you download from this site as well as the bit bucket repo at http://bitbucket.org/ellislab/codeigniter-reactor

MY_Controller and other extended libraries can now be put in the "core" folder inside your app. The user guide can help you upgrade.

I have been running Modular Extensions on Reactor for a few weeks now, works well. I am confident it would work in both branches though.