What is the difference between mkuser and useradd command in AIX?

Answer 1

The syntax is the only difference. Both accomplish the same thing and if you compare the man pages of these commands, you will see that they are effectively the same text. useradd is the 'standard' UNIX command for adding users, present on solaris, HPUX, etc. mkuser follows aix specific syntax that uses name,value pairs to define the attributes.