I preferred the director's cut, I thought it was sadder than the other one, that he would kill himself rather than let Kaylie have a bad life, and also the thought of realising that he wasn't ever meant to have lived.
I saw the director's cut first, then the other version on C4 and that didn't really seem to do the rest of the film justice, in that the whole thing was just resolved with Evan scaring Kaylie at a party.