We are using YSlow application and Fire Fox 6
Talking about the comparison of template of those companies:

• YOOtheme with Revista
• Rockettheme with Clarion
• Shape5 with Cyan
• YouJoomla with YouRetro
• Gavick with eSport
• JoomlaXTC with Barista

Rockettheme has just introduced Clarion - The Joomla! Template on Febuary 2012. Clarion is a subtle theme, really suitable for business. In another way, you can use it as a platform for extension individual customization. Using Gantry Framework makes Clarion more power, flewible and has lots of features as well as functions. The outlook of its front page seems very nice with easy control panel and customizing layout. Some of extensions belong to Clarion: RokGallery, RokNewsPager, RokTabs, K2 ...