In fact both panels are not comparable both in terms of usage and functional levels. If you want a control panel more towards shared hosting or multi accounts hosting, cPanel is your choice. If you have a personal hosting server which is application specific , you may check Webuzo. But cPanel shouldn't be too slow as said unless your server is overloaded or slow.
I would go cPanel 100%. If your cPanel is slow, you have some issues with the general server that need to be looked into. I would always go cPanel, every time over every other domain control panel. They run a very superior service to most, if not all other control panels.
If you are selling hosting yourself stick with Cpanel as that's what people are used to. If you use something else you will start getting tickets from customers asking why it isn't panel....
If it is for your website on a VPS or something then there is 0 reason to use Cpanel. But I would recommend VestaCP.