Linux is a modified version of Unix, most of the shortcomings of Unix have been removed in Linux and this makes it better then Unix. There are some other parameters where you will find Linux better than Unix and they are like, better user interface, better customer support, easily understandable, more effective and short commands, etc.
Unix operating systems were developed mainly for mainframes, servers and workstations except OSX, they are mainly used in internet servers, workstations.
Almost all the work that Unix does can be performed on Linux as well and even that with a better user interface.