Urethane may hold up better, HTH.
Have now had many hundreds of thousands of miles with poly and with stock rubber, and my observation is that yes, poly lasts longer, but not by much. In my observation, geometry (does everything line up just right?) and stresses (stock versus lifted) seems to play a bigger role than material.
Some of these observations are totally A/B (same rig, same suspension, just poly versus rubber) and other observations are at the same time as suspension mods. I have not observed any difference whatsoever in plain poly with grease versus graphite-impregnated poly with grease, and haven't tried graphite impregnated poly without grease. I also haven't observed any noticeable premature degradation of stock rubber with grease versus without grease, as I have read about over the years, although I did try silicone grease instead of dino grease for a couple years on a set of stock rubbers, didn't seem to make a difference.
My recommendations:
(1) Replace the bushings when they seem worn out.
(2) Price being similar, I'd go with poly, but if rubber was handy they seem to work fine. Either are good for 30-100k miles, depending on useage, how far you are from stock, and alignment/fitment.
(3) I don't think poly is worth a significant price premium, and especially graphite-impregnated.
(4) Suspension work is such a large amount of work, particularly for leaf suspension, pay most attention to fitment and alignment.