I've been in the Hosting industry coming on close to 12 years as a systems administrator working for various hosting companies and data centers before GeekGhost. I am personally also cPanel certified. From my experience, cPanel all the way. I've used and installed Plesk, H-Sphere, DirectAdmin as well as others and for the money cPanel is the way to go. Really intuitive and easy to navigate on the clients' end and makes migrations to cPanel from most other control panels a breeze thanks to cPanel's migration service. Of course, if they're coming from another cPanel host it's as easy and entering info in to a few fields and clicking a button. Everything gets migrated.
The DNS clustering feature is pretty great. We have DNS servers that serve DNS for all production servers and each server runs its own DNS as well. With DNS clustering we can easily move accounts around if needed with zero to very minimal downtime. It's what also allows us to split reseller accounts between two data centers if that's what the client requests.
The ability to create themes or brand the existing theme is a nice touch as well.
When all else fails, cPanel support is top notch and second to none. Quick resolutions and knowledgeable techs. Couple that with the immense community support and most issues are very easily resolved.
From a server administrator's perspective managing several servers I wouldn't go with anything but cPanel. Makes life easier for the client and the admin.