I've only used Plex, which I found to be quite straight forward to set up. (I used the plugin the first time I set it up, but after suffering through an incredibly long—though successful—upgrade, I switched to a manually created jail and installing Plex via pkg.)
I have seen complaints from people who wish Plex handled music better. If Music streaming is important to you, then that appears to be Subsonic's forte.
Firefly, while dead as a project, is still widely used as most music clients support either DAAP or RSP protocols. There is also a forked rewrite of Firefly and an upgraded multi-threaded version available, see http://en.wikipedia.org/wiki/Firefly_Media_Server
for details and links.
As to Plex vs MediaBrowser, the top couple of results from a Google search led me to stick with Plex, but MediaBrowser has features that Plex users have been asking for for years. (In particular parental controls.) A few minutes reading should quickly allow you to choose which is best for your needs.