It depends on what do you want to achieve. C++ chrono pros:
- Better understandability (more users know standard library than boost)
- Better portability (in case you have decided to use c++11)
- Maybe it will work faster.
- Don't add additional dependencies to project.
Boost chrono pros:
- Works for c++03
- Provides more functionality.
So, if you don't need that additional io functions and don't need c++03 support, use standard library.