I once had the opportunity to test all control panel systems on my test VPS. So here is a brief overview of my experience just in case anyone should need a concise overview. It was based on a fresh Debian Lenny 64bit system.
SysCP: Probably the slimmest of all control panels. I liked very well, because it is actually perfect for a VPS with a handful of domains and hardly more email addresses. But also for commercial hosting SysCP is to use; thanks to ticket system and various user levels. The installation was pretty easy, even when the manual to change the config files is a bit time consuming. However, I wanted to send the mail postfix part out not (but probably was more like gadgets than on my previous SysCP ).