I created and led the development of Formula One VBX / ActiveX / Java for more than ten years. I left to start SpreadsheetGear LLC shortly after Actuate acquired Tidestone Technologies in May of 2001.
We released SpreadsheetGear for .NET 1.0 in 2005, added support for xlsx (Excel 2007) workbooks in version 4.0 and added support for Excel 2010 xlsx and xlsm workbooks in version 6.0 last year.
We are confident that you will not find a more Excel compatible spreadsheet component than SpreadsheetGear - but obviously we are biased so you should try it for yourself.
You can learn more here and download a free trial here.
Disclaimer: I own SpreadsheetGear LLC