I chose the Bucharest version. Honestly, I haven't picked up the 4th Wall yet, but I can't imagine that the version of Scarred on there will be my favorite for one simple reason - it's pretty much the studio version. For me, I love all the extras that the band used to throw in to some of their songs, and it is evident from the other versions listed, each time Scarred was part of the master setlist, they did something extra with it, aside from the current tour.
JP's intro guitar spot always was a great lead-in to Scarred on World Tourbulence, and the inclusion of the instrumental half of IF was cool too, altho I personally preferred when they tacked on Rush's 2112 Grand Finale, as they did at most shows earlier in the tour.
The version on OiaL doesn't get any consideration from me only because it's an abridged version, unlike what was played that night - I'm pretty sure this was done so that they could fit more stuff on the first CD. Had it not been abridged, it would probably be just below the CiM version in my rankings. And I really do like the version on CiM, but the one from the Bucharest DVD edges it out.