Vlc is also a good multimedia player capable of transcoding formats as is done by mencoder. The decision point may hinge on qt vs gtk libraries. I use mplayer without a frontend on my lightweight systems. If I have qt, say from installing libreoffice or stellarium then I use vlc.
If you are installing in NetBSD 2 versions of vlc are available. The older version was gtk based (<=0.9.8) and the newer versions (>=1.0) are qt based.
Another point of consideration was the audio backend. Vlc has had sndio for sometime and mplayer just had its sndio backend
"polished".