From the start of the "poly craze", promoted by magazines with advertisers of such (it seems), after consideration, I came up with a "mix" orientation. For suspension parts which just pivot (as in GM or other upper control arm bushings), then poly might help locate them better for a little better handling precision. But for bushings which absorb road forces, as in the lower control arm bushings (typically GM and such), then rubber is best in those locations. I suspect that all replacement bushings are of higher durometer (stiffness) than the OEMs might have been, too. Front leaf spring bushings should be rubber, but the rear shackle bushings can be poly, as with the mounting pads for the rear springs-to-axle housing.
Key thing is that there are places in the suspension and body structure that NEED to have absorptive capabilities so that these forces are not transferred to places they were not designed to be (in the chassis and/or body).
On the cars with link-bolt sway bar attachments to the lower control arms, POLY finds a great place there. Supposed to make the sway bar act 20% stiffer, than with the stock rubber bushings from the factory. Moog sells them in the complete kit (blue bushings), which seems a bit softer than the white bushings which GM sold for the WS6 '79 Firebirds.
Enjoy!
CBODY67