Originally Posted by hassanali_2009
the Linux distribution I should use and master it so that I can become an expert specifically for that Linux distro, that will definitely help me in my career growth.
The only common way becoming expert in a specific
Linux distribution makes sense for "career growth" would be for career growth in IT and the specific distribution would be Centos. (Learning Centos well qualifies you for IT support at the large number of companies using RHEL as well as those using Centos).
Many other Linux variants are used by many companies, but none of the others stand out as the specific one to learn in order to qualify for Linux IT work.
But if the work you have in mind involves using or programming on Linux systems, rather than doing IT support for them, there is no specific version. The differences between Linux distributions matters primarily when installing and maintaining them. Those differences are pretty trivial when using or programming on them.
If you want to learn to use Linux or program on it, select a distribution that is easier to install and maintain. I suggest Mepis. Ubuntu is similar to Mepis and much more popular and, like Mepis, is easier to install and maintain than most distributions. But I think Mepis is a little better and easier.