We have tried Aspose.Words for .NET libraries and the richness of supported file format is very impressive. Additionally, the performance is beyond my expectation comparing to other commercial products out there. The Word files generated by our application are not only created faster, they are more like what our customer's want.  It also has easy to understand interface so that I can integrate to our application without too much difficulty.

We have changed our process in order to eliminate Microsoft Word software dependance forced by the native Interop libraries. With the Aspose library we were able to manage all the process in memory and manage the document more efficiently. The objective is double :

1. Avoid the installation of Microsoft Word on a server for automation purposes
2. Better performance with a library directly in a code

Also, Aspose has a complete Microsoft Office library and is very useful to add some flexibility and functionality to our web application. Your mileage will vary depending on the methods used to process documents in regards to integrating their library, but they are functionality complete and the documentation is an integral part of the provided product.