I usually bite my tongue about this - but since you asked: Youtube is definitely frowned upon - almost as bad as MySpace. Personally, I don't even like soundclick, unless there's a "download" link right there on the page...in which case I would have preferred to have been given that link to begin with.
The idea here was to post an MP3 file - and I still like that the best on the rare occasion that somebody does that. Not one that we have to register for or jump through any hoops for the privilege of downloading, mind you. Just click, download, play, analyze, offer feedback - no fancy trickery, no requirement to have a video playing while listening, no requirement to listen on a certain machine that's hooked up to the web (some guys don't allow their DAW on the Internet... kind of archaic idea, I know - but it's still clung to by some).