There are 3 types of cleartype: WinXP’s Cleartype, Windows Vista’s Cleartype and Windows 7′s Cleartype (the same as Windows Vista) and Windows 7′ DirectWrite Cleartype.

By font rendering DNA:

Internet Explorer v6 to v8: unknown + cleartype
Internet Explorer v9: unknown + cleartype + directwrite
Chrome: freetype + skia + cleartype
Firefox v3: freetype + cairo + cleartype
Firefox v4: freetype + cairo + harfbuzz + cleartype + directwrite
Safari: quartz or cleartype (by default in recent versions is cleartype)

As you see very complicated. The best rendering is with Windows 7 + Firefox 4. The worst is Chrome, awful font rendering!

Directwrite on windows is an improvement but only Firefox 4 and Internet Explorer will be using it.

I never use fonts as specified by the web designer. I always override the defaults and choose to use my own fonts.

The best fonts for windows are fonts designed specially for windows. In Windows 7 case is Segoe.

The worst about web fonts is that they will not use neither hinting or kerning. Web fonts are unnecessary. Let the choose the font. It will always be the best solution, since the designer can’t control everything given the diversity of rendering alternatives, display/monitor quality and size, and users’ eye problems.

You should lobby the web browsers manufactures to make it easier for their users to choose their own font!