What is the 'best' Content Management System for low visits?

I need to build a website that keeps the content & appearance themes separate. I figured that a content management system is the best way to achieve this goal. I expect the user base to be hundreds of hits a day. What is the best content management system for:

• Speed (given the low visits)
• Development & maintenance (cost of hiring developers & maintaining the system, ability to upgrade to new versions of the system while keeping my customized code separate)
• Availability of free themes

Check some of these babies out.

• Wordpress or Joomla! (if you're on PHP)
• DotNetNuke (if you're on .NET)
• Pinax (if you're using Python)
• Radiant (if you're on Ruby)