Best .NET Framework compression class?

GZipStream and DeflateStream are specifically intended for compressed streams, not general compression of files for storage.

Other than those classes, compression is not built into .NET. If you want high-quality compression you will have to go to a third party library. Check out http://www.7-zip.org/sdk.html for an open-source 7zip library.

There is a managed wrapper for 7zip. The license is LGPL so you can use it in closed source projects. I do not know if this fits your license requirements as you did not state them.

http://sevenzipsharp.codeplex.com/