Function, you cannot 'RIDE' a toy bike! i.e. 'Flat specific' set-up we've come to know so far...
Ergonomically a "flat specific" bike serves a better function than a "street looking" bike.
However a street bike often has less aggressive geometry that allows for grater comfort of "Riding".
Which in those aspects would put oldschool frames (Hutch pro raider?) in the top spot for having smaller geometry in the front end, roomier in the rear and a double diamond shape for aesthetics.
I just wonder how my PIR frame would measure up on this scale as technically it has an even simpler design than that of a double diamond frame. With greater relaxed geometry but looks very different in terms of aesthetics (many would say in a negative way)