Here is why we use (and recommend) WebSitePanel (WSP)

WebSitePanel Parallels Plesk Panel
Fast and easy to use streamlined interface
Next generation advanced control panel architecture. Each service (DNS, web, mail, database, etc.) runs on separate physical server for improved performance and reliability
Ability to create custom DNS servers and override the default DNS servers (resellers)
Ability to create custom hosting summary (resellers)
Ability to use one FTP account for all domains under the user account
Ability to have multiple packages (shared hosting, VPS, cloud) under one account and control them from the same control panel
Support for .NET Framework 4
All application pools can be setup in both Classic and Integrated modes
Ability to create custom errors, headers and mime types in IIS for each domain
Support and control of IIS Remote Manager through the control panel
Ability to create custom hosting plans (resellers)
Advanced mail server support - Smartermail 6.x
Advanced statistics support - Smarterstat 5.x
Ability to upload databases backup via FTP.
Ability to restore uploaded databases directly from the panel
Support for zip archived database backups
Support for zip archives in the panel Web File Manager
Ability to use one database user for multiple databases
Ability to create multiple scheduled tasks - i.e. Database only backups, check site's availability, etc.