I aim to start opencv little by little but first I need to decide which API of OpenCV is more useful. I predict that Python implementation is shorter but running time will be more dense and slow compared to the native C++ implementations. Is there any know can comment about performance and coding differences between these two perspectives?
You're right, Python is almost always significantly slower than C++ as it requires an interpreter, which C++ does not. However, that does require C++ to be strongly-typed, which leaves a much smaller margin for error. Some people prefer to be made to code strictly, whereas others enjoy Python's inherent leniency.
If you want a full discourse on Python coding styles vs. C++ coding styles, this is not the best place, try finding an article.
EDIT:
Because Python is an interpreted language, while C++ is compiled down to machine code, generally speaking, you can obtain performance advantages using C++.  However, with regard to using OpenCV, the core OpenCV libraries are already compiled down to machine code, so the Python wrapper around the OpenCV library is executing compiled code.  In other words, when it comes to executing computationally expensive OpenCV algorithms from Python, you're not going to see much of a performance hit since they've already been compiled for the specific architecture you're working with.
Does performance differ between Python or C++ coding of OpenCV?