which is best text editor is available to use with silverlight.
I’m not sure I understand what you are referring to.
Are you asking about development-time tools? We use Visual Studio and occasionally Expression Blend.
Are you asking about run-time text editors within your Silverlight application? You can use what Silverlight provides, or you can find enhanced editors on the Internet. I don’t think we have any experience with editors other than what Microsoft provides for Silverlight.