There are two main flavours, the DC (1992 directors cut) and OV (1982 original theatrical version) with a few differences between them, but both equally good IMHO. The OV has a couple of extra violence scenes, a voiceover by Deckard (Harrison Ford) and a sappy ending whilst the DC does away with those leaving you with an amazing film, especially with the Vangelis soundtrack he created just for the film.
The DC is on official DVD (out of print in the UK) but was one of the first films put to DVD and the picture quality isn't so great, whilst OV has only been released on VHS/laserdisc - hence the various DVD transfers of the LD.