I didn't vote but here's my experience with the two.
I run ES poly mounts on my Mustang and they work great. I can't really say if they added any appreciable vibration to the chassis though as I installed them with a tubular k-member and solid bushing everything. They do they're job fantastically though and while revving the engine from the engine bay, the motor has virtually no detection (<1/16"). Under a load however, it may be different.
Several years back (damn, was it that long ago?!?), I had a 5.0L Ranger that I installed solid mounts on. The truck was a desert beater, had no interior, a fiberglass bodywork, and a ton of suspension work. After installing the solid mounts, I was constantly having to go through and tighten up every fastener on the damn thing (until I started safety wiring the critical stuff). After going back to rubber mounts, the problems stopped. Since the truck was consistantly being beat on (jumps, washboard roads, the occasional mud pit run), I'd imagine that the solid mounts just compounded the vibrations from the motor. Your results may vary.
For what it's worth, a guy with solid mounts in his Mustang drove mine and said he couldn't tell the difference between the solid and poly bushings.