Hi Asmita,
I think first try to define what you need. Based on that you can choose from the available options.
PANS is a complete RTLS build for DWM1001 while MynewtOS framework has a different focus. eCos or Mynewt here is not too important IMO. eCos has been chosen only because we had knowledge of using it. But it is obsolete. If you decide to build a new system, then I would recommend to choose something else, e.g. MynewtOS or Zephyr (see this post DWM1001 & Zephyr: open source port + example code).
Cheers,
TDK