Which is the Best Free Load Testing Tool?

We have been assigned the work to find the best Load Testing tool from Free Tools domain. We also need to evaluate it against some best paid tools. Requirements were:
  • Tool should be free and preferably open source
  • It should be very stable and mature
  • It should be able to generate any amount of load without any software limit. Hardware can be increased as per requirements. 
  • It should be able to generate the concurrent load in concurrent running threads
  • It should support running JUnit test cases out of the box
  • It should support recording of Test Cases for UI, which can be played back later with load
  • Generated reports should be extensive in information and preferably in format also
  • Tool should be in active development
  • Out of the box support for various other interfaces will be a plus
With explorations, we found following tools famous and highly recommended in their categories:
  • Apache JMeter - Free and Open Source
  • Grinder - Free and Open Source
  • HP Load Runner - Paid, just to have a good comparison
Our exploration for above three tools is: