I've always noted that I prefer breasts that have wide coverage.
By this, I mean, I like a large left-to-right dimension, and a high correlation between connection-zone and depth of unconnection-zone-tissue. If that makes sense. Breasts that have a big gap between them are unattractive to me; and breasts that dangle are also unattractive, unless they also are large enough that the part where they touch the ribcage is also large.
So, I guess I'm arguing for classical proportion, mostly independent of size.