cPanel/WHM - It's more or less the standard when it comes to hosting it seems. Sometimes buggy (better to stay on the stable versions), bit of a resource hog but hard to get away from.
Interworx - New kid on the block. Very nice integration of DNS, APF Firewall, IP management, other nice features. Missing some basic stuff like mailing lists. If you're starting a new account you can probably get by with some workarounds. If you're moving a lot of cpanel sites over, it can be a nightmare. Less resource intensive than cpanel, very nice frontend.
Interworx - New kid on the block. Very nice integration of DNS, APF Firewall, IP management, other nice features. Missing some basic stuff like mailing lists. If you're starting a new account you can probably get by with some workarounds. If you're moving a lot of cpanel sites over, it can be a nightmare. Less resource intensive than cpanel, very nice frontend.