If you don't mind home appliances, then the Synology one is the best I have experienced. Easy to use, stable, one click installs for everything, intuitive. It does the desktop metaphor but unlike all the JS libraries I've come across this one doesn't appear to lag. Well suited to its application.
In terms of server management, er probably none of them. Including the web based ones like cPanel, webmin and Plesk. OpenPanel has pretty screen shots, though you don't want to read phrases like "Please note that OpenApp always expects a clean install! Installing OpenApp packages on a non-clean system is likely to lead to data-loss or a non-functional system" so I wouldn't actually install it. All the ISPs present bottom-up approach to management, making it piecemeal. I'd rather have a top-down approach.