ScreenFlow has proven to be good so far, but has also caused us to lose important content due to corruption and some times simply not working.
The built-in QuickTime Player bundled with the latest version of OS X can record desktop videos is a nice free option. File>New Screen Recording. It does depends on how much detail you want to show. Screenflow is nice in that it allows you to zoom in on the screen after the recording for details without losing resolution. Many of the other options out there lock in the resolution at capture. So if you go to zoom into say a particular area of the screen later, it will lose resolution due to the scaling and lose some detail.