If you're looking for a simple, yet powerful hosting control panel, Vesta could be the one.

Install: it's a one-liner, they have a script that takes care of everything

Usage: this panel can be used by both experienced sys admins and regular users, the design is very clean and fluent

Performance: it's using a Nginx reverse proxy to Apache configuration, so you'll not end up with dropping connections on traffic peaks

API: you can script various actions like mass-adding sites by using their API interface