A practical example: suppose you have some postfix log and have to create a report of the most often used sender-recipient pairs. Probably the best way to do this is to create a hashtable, containing sender-recipient pairs as keys and the number of occurences as values.
To implement it in bash you lack pretty much everything, you don't have hashtables, you can't easily handle pairs and even to increment a counter you have to use some pretty wierd expression.
However if you have python you have all these structures and can handle every aspect of the problem out-of-the-box. So this problem is much easier to solve in python.
Another example would be to simply check if a specific sender sent an e-mail today. In bash you can just use "grep sender maillog" and you are done. In python you have to create a way longer script to achieve the same. So in this case, bash wins.
Choose the tool that best suits your needs. From the five options, I would focus on bash and python, they pretty much cover everything.