The answer will depend on what you want to get out of it.
If you are looking to expand your skills and understanding of Linux to be put into use in the corporate world, you need familiarity with RHEL. You can download CentOS for free as it is a downstream version from Red Hat.
Personally, I have been using Linux as the OS on my personal laptop for years. I am a big fan of Debian and I have found that Linux Mint Debian is a good distro that tends to "just work".
Download - Linux Mint