Generate Reports in Excel without Office installed in server.

Question

Hi,
  I have generated the reports in excel using Msoffice but cannot generate in my server due to security issues,so..
   i want to generate excel Charts without using excel.interop  library.
I googled then i found all these are open source but each have its pros and cons ,NPOI ,Open Xml SDK 2.0,EPPLUS,Excellibary.
 
   our project has about 20+ reports to generate,with different chart types.

can u please suggest me the best open source to generate reports in excel with better performance.
Urgent....
Thanks.
KK