YouTube to MP3 is 100% legal though, as long as you're not distributing the songs to other people. They should be cracking down on sharing sites instead of this.
Some people actually use these to get remixes/explicit versions of songs that aren't on iTunes.
But I also use it for Soundcloud links as well, so it's not strictly at YouTube-to-MP3 site. But yeah, I only do it when there's absolutely no where else to download a song.