there are a billion threads on this topic.
depends on what you want to do, how much control you want to have, if you like to tinker, or if you just want something to set things up for you.
you usually get less bloat and more control with distros that you have to tinker with, but they also dont offer much in the way of hand holding.
personally, i think debian is a good combo of ease of use and performance, great package management, and tons of stuff.
you have to add other sources to your etc/apt/sources.list to get some things you may want for mplayer.
just search these forums when you want to set something up. 90% of the questions you will have have already been asked.
also explore different distros websites and read reviews, or, since they are mostly free, download a few iso's and try 'em out.
for more info on whats out there,
have fun !