We've had this debate a looooong time ago and no matter how many pics I see and my own hand-held comparisons...I still think the Sideshow Buck body is at the bottom of the pile of the "Big 3".
But Sideshow claims they are doing R&D on a new body style...perhaps we'll see something in 2008 in terms of that.
What Sideshow SHOULD do if they do create a new body is make sure that they at least offer or use the same neckpiece (and maybe even a wrist adapter if they change it) that the Art S. Buck used so that people who bought all these older figures could easily convert them over to the new bodies.
Though more profit could be made by Sideshow if they just perhaps remold some pieces and re-release figures on the new body.
...but they didn't hear that from me.