Obviously Python is more user friendly, a quick search on google shows many results that say that, as Python is byte-compiled is usually faster. I even found this that claims that you can see an improvement of over 2000% on dictionary-based operations.
What is your experience on this matter? In which kind of task each one is a clear winner?
Developer efficiency matters much more to me in scenarios where both bash and Python are sensible choices.
Some tasks lend themselves well to bash, and others to Python. It also isn't unusual for me to start something as a bash script and change it to Python as it evolves over several weeks.
A big advantage Python has is in corner cases around filename handling, while it has glob, shutil, subprocess, and others for common scripting needs.
Bash is primarily a batch / shell scripting language with far less support for various data types and all sorts of quirks around control structures -- not to mention compatibility issues.
Which is faster? Neither, because you are not comparing apples to apples here. If you had to sort an ascii text file and you were using tools like zcat, sort, uniq, and sed then you will smoke Python performance wise.
However, if you need a proper programming environment that supports floating point and various control flow, then Python wins hands down. If you wrote say a recursive algorithm in Bash and Python, the Python version will win in an order of magnitude or more.