This is not a good comparison. If you want a good mp3 player, go with the Zune. The Galaxy really wouldn't serve as a good MP3 player. If you want to use it to go on the web a lot, check email, and play games, I would go with the Galaxy.
I have a Zune HD and love it, I have an EVO 4g and love it, and I'm debating on getting a tablet. But it's between an Ipad (ugh) or maybe a Viewsonic 10 inch, just because I want a 10 inch screen.