To me, the availability of professional support is at least as important as the extension itself. The guys at ChillCreations seem to know that and act accordingly. And they're fast... Recommended!
For me, there's no site delivered without Akeeba Backup.
We develop lots of Joomla websites and this powerful component is exactly what is lacking from the Joomla core. From the very beginning ACL Manager already was a ★ Huge Time Saver ★ Now with the clickable permission grid it's like magic spell. A must have for every web developer!