What is the difference between adduser and useradd?

useradd is native binary compiled with the system. But, adduser is a perl script which uses useradd binary in back-end.

adduser is more user friendly and interactive than its back-end useradd. There's no difference in features provided.

Source: What's the difference between “adduser” and “useradd”?

Always use adduser (and deluser when deleting users) when you're creating new users from the command line. (If you're writing a script, especially if you aim for portability, you might want to use the lowlevel utilities instead – and adduser/deluser might not be available on all distros, e.g. on SuSE.)

The useradd, userdel and usermod commands are lowlevel utilities which are there for historical reasons, while adduser/deluser Do The Right Thing™. (I remember which to use by thinking that user* comes after adduser/deluser in the alphabet, and therefore is "worse".)

According to the respective manpages (on Ubuntu 12.04 Precise Pangolin, i.e. a Debian derivative system).

Manpage for adduser says:

(Emphasis added.)

adduser and addgroup add users and groups to the system according to command line options and configuration information in /etc/adduser.conf. They are friendlier front ends to the low level tools like useradd, groupadd and usermod programs, by default choosing Debian policy conformant UID and GID values, creating a home directory with skeletal configuration, running a custom script, and other features. adduser and addgroup can be run in one of five modes:

Manpage for useradd says:

useradd is a low level utility for adding users. On Debian, administrators should usually use adduser(8) instead.

See also: What's the difference between “adduser” and “useradd”? (on SuperUser)

adduser: add user with full profile and info (pass, quota, permission, etc.)

useradd: add user with his name only (if you want to add a temp user with only a name,other info not required)

Another couple of differences, that lead to specific scenarios where useradd might be preferable.

1. In some newer distros, including Ubuntu 14.4, adduser will prompt for information such as password and "gecos" (data for the finger command). This means it can be less suitable for calling from a script (credit: already mentioned in a comment by Wernight).

   The prompts can be suppressed by passing null arguments:

    adduser --disabled-password --gecos "" USER
   

2. useradd allows you to pass multiple additional groups to add a user to by means of the -G option. adduser seems to require that you call the command once for each group to add.

adduser is friendlier in that it sets up the account's home folders and other settings (e.g. automatically loading system stats and notifications on login), whereas useradd just creates the user.