I don't know if anybody cares (seems to be very windows-centric discussion

), but for Linux the best media player is mplayer, IMO.
Xine is great because it's set up for you use to easily, Totem should be cool, but the gstreamer framework its going to use is still in heavy developement.
It's got a dozen different ways to do deinterlacing, it supports most codecs in existant that I am aware off.
Its gives verbose details about the type and content of the files that your working with. So you know what your dealing with.
For example: you know quicktime is just a wrapper, that it has many other codecs encased in one codec. For instance you can even do weird things like have mpeg2 video and mp3 audio embedded in quicktime... Each quicktime version is very different from the others.
That sort of thing.
It has a few different ways to deal with audio and video. Depending on your setup it can handle almost a dozen different video outputs. For example you can output the video into a OpenGL window, or use XV extensions to take advantage of your accelerated video hardware. It can output the video to a file, or even create neat thing like a text-based (aa) video output or even a color one (caca), which is a funny thing to watch.
sample screenshot of libcaca in action (not from mplayer, though) (you can get it for windows, too)
So if the color seems off, or you want more control over the output or you need faster output you can pick and choose which setup works the best for your paticular computer.
Pluss it supports Windows codecs, so you can copy the proper *.dll files from windows installers/partition and put it in a certian folder (so the program can find it) and it can use it if it supports it.
I can play most versions of quicktime on it, I can play realvideo (pretty sure) and realaudio(definately), as well as stream mp3's, ogg, and mpeg files thru the internet. Also supports many unusual and esoteric formats.
Plays DVD's (even encrypted ones if you have libdvdcss stuff installed (doesn't come default in some distros sometimes because if legal issues) and CD's and most whatever else you want.
You can feed it http and other protocol links via copy and paste and it can handle them. Lots of times I've read thru javascript and http crap in links and webpages and extracted links that otherwise I would have to have signed up to get.
It's not user friendly with nice menus and such, the best interface for it is text command line, but to me it seems like the ideal tool for a media junky to use.
linky if you care
Oh, and Mplayer is mostly for movies, XMMS is what I use for Audio. I use Totem and Zinf when I want to mess around with playlists, though.