The worst kind of backtrack is a midi file converted to an audio track. Probably not quite OK from a copyright perspective, but as long as you don’t make any money from them I figure it’s morally fine (record labels: I’d be happy to pay for backtracks like these! Please sell them!). They are slightly more common now though compared to a couple of years ago, as they can be made by ripping the individual tracks from Guitar Hero or Rock Band. These are quite hard to come by as no artists (at least that I know) release such tracks officially.
The best backtracks are originals with all other tracks, even vocals.
songs with no guitar tracks that allow you to jam over them yourself or make a cover of a known song. There are numerous sites for backtracks (like and ), i.e.
