(1) Build in billing system
(2) Domain Reg (Enom/OpenSRS API)
(3) Built with Java
(4) Supports Linux and Windows and you do clusters
(5) psoft is excellent
(6) Knowledgebase within the control panel
(7) Trouble Ticket in the control panel
H-sphere = cpanel + modern bill + drams
(1) Licensing is a bit steep $4.50 per account. You can find cheaper lic from their resellers.
(2) Recurring billing for 2checkout does not work well. First billing has to be manual then you have to inform your clients to pay next month.
(1) Many Skins to choose from
(2) Many customers are used to it and like it
(3) Cheaper Lic than h-sphere
(1) Saturated. Everyone is selling hosting services with cpanel. This doesn't make you special anymore. ... Just another cpanel host.
(2) Want to sell domains with hosting? You're out of luck. You will need drams or some other scripts to help you with it.
(3) You need a helpdesk, knowledgebase, an online billing system, you need to look elsewhere. i.e. Perlbill, Autopilot, ModernBill, PhpManager
I can't speak for Plesk, sphera, HELM, ... ,etc
Jburnley, so to make a Super CP, I think H-sphere and cpanel strenghts combined can make a killer control panel.