I would just echo what everyone else has said.
In fact, I have dont both, depending on the situation.
<a href="
http://www.animemusicvideos.org/video/162704">58008</a>
With this video, while I did follow the lyrics to some extent when making my video, the lyrics aren't the main point here. If someone wants to look up the lyrics on their own, maybe they will get a bit more out of the video, but it is still perfectly possible to enjoy this on its own, without knowing the lyrics at all.
<a href="
http://www.animemusicvideos.org/video/184230">All I Can Do</a>
But with this video, I chose to subtitle it because the lyrics are absolutely critical to the understanding of the video. My video follows every single line of the song, and without having those lyrics available, one of the primary elements of this amv would be lost.