Which is better to learn Linux or Unix?
Linux is far more common these days than traditional Unix. But
as any old system administrator will tell you, learn to learn,
don't learn the system. There are numerous differences between the
different Linux distros, differences between Linux and Unix, and
differences between each of the Unices. Learning everything about
each system is a daunting task, and probably near impossible.
Rather than, say, learning all of the different command line
switches for "ls" on each system, just know how to access a man
page.