On the E30 type suspension I think that poly rear subframe mounts are a must. Other poly bushings are fine, and do help out a track/autocross oriented car. However if you street drive the car, poly bushings are a bit harsher.

Delrin and solid bushings are best for track only cars, that are seldom street driven. LOTS of NVH (noise, vibration and harshness) and more maintenance as they need to be lubed and checked for wear.