Seeing as we are mentioning the prequels I'll mention my favourite versions of those:

TPM: Ady' theatrical reconstruction. I hated the DVD new additions and colours and Ady's version takes me back to when I saw TPM at the cinema.

AOTC: IMAX version. There was a bootleg copy of the IMAX version circulating around the time AOTC was out which I consider to be the better version but unfortunately no longer have it. 8(

ROTS: I don't really have a favourite right now. I haven't watched it properly since I saw it at the cinema, and have been waiting for the ultimate edit of this movie, as I feel it had a lot of potential wasted. Currently patiently waiting on bobgarcia's "Reign of the Dark Side" fanedit.

Personally can't wait to see if people's lists change over this year with so many preservations,edits and then finally the blu-rays coming out. 8)