The one that became popular on the radio (and is a much better song) is the remix. In fact, the Sneaker Pimps started including that version (along with the original) on their CD release.
However, that's a fact that I happen to know (because I have the CD and know the background), but others don't. So I think that when anyone picks that song, they're wanting the remix, without necessarily knowing that.
YouTube calls the original the "album version". It's higher pitched, and lacks the added rapping effects:
This is the "official video", which is the remix (you can hear the rapping and added sound effects). This version has more "gravitas".