Media players are applications that handle the playing of audio and/or video. (In this comparison the listening of music will be the only factor, not how well/if these applications can play video.)
There is wide debate over which media player is superior, and this will list some of the pros and cons of each media player. Of course a lot of information is left out and of course there are a lot more than are listed, but this article will point a media player-hopper in the correct direction.
Clementine can stream music from the internet and sync with devices. Common media player characteristics are included, such as shuffling and looping.
One of the selling points of Clementine is the ability to destroy the main window and have it reduce to the notification icon. From there you can control the volume, pause, play, move to next track, move to previous track, mute, love, ban, quit, or show the main window again. Clementine also integrates into the Ubuntu sound menu.
Amarok is also capable of working without the existence of the main window. It will fall back to a notification icon with previous, pause, play, and next options as well as the option to show the main window.
3. VLC Media Player
VLC is a popular music player that is very good at what it does. It specializes in streaming but can also be used as a general purpose music player. If I have files that I do not want in my common playlist I use VLC since it does not save playlist information through usages. VLC does not excel with audio playback, but is rather used a video streaming/viewing application.
VLC, like Amarok and Clementine, has a notification icon but it cannot live without the main window. VLC has a very good equalizer
Mplayer has frontends available for it, like SMPlayer. Mplayer by itself does not work with the mouse, so you must memorize the keyboard commands to use it. Some find mplayer to be the best way to listen to audio since you can run it without a window or notification icon at all if you so please.
Interestingly enough, mplayer can play videos very well and is my video player of choice.
The Media player does not offer much in the way of customization or organization like Clementine, but it does get the job done like a media player should. It can import / export playlists, list statistics about the current playlist, and most importantly live without the main window and run as a daemon from the system tray. If you want to use Clementine without the elevated RAM usage and superfluous features, DeadBeef is the media player for you.
I did not include the following popular media players:
Banshee: Rhythmbox does nearly the same thing as Banshee.
XBMC: "VIM is a text editor; Emacs is an Operating System" is my favorite quote regarding text editors. XBMC is the Emacs of text editors. It is its very own ecosystem and would not be practical to use for multitasking. This is definitely the choice for a user wanting a heavily media-centric computing experience.
I cannot call the conclusion fact since all of these media players do exactly what they are supposed to: play media. I just feel that Clementine has the best functionality. It can run in the background or have the main window; it doesn't matter to Clementine. It also does everything that Amarok can do like sync devices, fetch data, and live without a main window, so the presence of those features somewhat invalidates Amarok.
Bear in mind this opinion is only based in audio, and for video mplayer is my choice. I have no justification for this and VLC does just a good as job as mplayer.