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

• Yootheme with Catalyst
• Rockettheme with Visage
• JoomlArt with Kranos
• Shape5 with Sienna
• YouJoomla with YouPlus
• JoomlaXTC with BusinessClass
• Gavick with Music

Sienna is a stunning Joomla Template with many great features to help you stylize your site exactly how you want it. With an amazing four highlight colors the color pallette of your site is in your hands! Highlight colors will transform the look of titles, backgrounds, modules, logo, and so much more. This is done very easily through the color picker built into the Vertex framework!