Well, I guess you can try any of these for Video.
http://www.linuxsoft.cz/en/sw_list.php?id_kategory=18
or these for Audio.
http://www.linuxsoft.cz/en/sw_list.php?id_kategory=14
For Video I use to use mplayer, but I think the default that comes with ubuntu is totem,which I think is a frontend based up xine/gstreamer,
I now use VLC, remember VLC on windows?..it was pretty good, it plays everything and anything.
For audio I use to use xmms, which was pretty damn good, I would say. I don't have it currently installed as haven't really got around to it.
As far as customization and features goes, I'm not sure which is the "best", as i really haven't put much thought to it, because I don't really watch Videos or listen to Audio on my computer.