Now I have to vote for 86/87's. Though I don't think its right putting the 86's & 87's together, as they sound completely different! 86's make a "droning" sound, and I always remember when a 86 arrived / departed Liverpool Street, as the sound resounded through the station. As for when they were moving, they weren't that loud, and didnt scream as much as sevens. Sevens on the other-hand werent that lound when going slow, and did not "drone", but made a pleasant humming sound. . . . but when they were moving it was another story.... .that wonderful screaming sound.... It was heaven..... I dont know what it was exactly, but I know 86's didnt really make it. As for 90's, I assume it is to do with the Thyristor that they dont make much sound....?, but I still rate 90's, though obviosly not as much as the sixes or seven's!
James.