Which Silverlight Rich Text Box to use

SL4 now contains a Microsoft implementation of a RichTextBox. This is awesome but doesn't support bullets, numbering, super script or subscript.

There are also a bunch of other RichTextBox implementations out there from the control providers.

When is the best time to use the Microsoft one and when should I go to the market? What is the best control for the 开发者_C百科different use cases for a Rich Text control?

BTW, I'm not looking for subjective stuff. I'm interested in functionality, performance, extensibility, download size etc

performance? Forget about Microsoft`s RichTextBox. The WPF RichTextBox is a speed mess because its a FlowDocument. Silverlight is not different.