libxine is generally better than the alsa Link I find. So if I have a choice between the two I go for the former.
The alsa jack plugin works well for boodler and I am told it works well for skype. It doesn't seem to work well for movie players and the like - nor have I been particularly happy with mplayers jack interface. (VLC doesn't do jack on Ubuntu and I can't be bothered building it from source)

It would be really nice if gstreamer and pulse-audio played better with jack.