I'm seeing a number of Open Source libraries on CodePlex (e.g. NPOI, EPPlus, ClosedXML, etc.)

My requirements are that I need to read and write Excel spreadsheets and they might be in the old XLS format as well as the newer XLSX format.

I see that NPOI says it supports XLS, XLSX, and DOCX where as the others don't support XLS.

Suggestions?