[bret]

In reality you can use either. If you're really going to chase the autocross and road course thing, use the heim ends. They eliminate the last little bit of flex and allow that last little bit of articulation. Our heim ends are Kevlar lined and stay tight and rattle free.
If you're doing a few events per year, just stick with the poly ends. They do eliminate just a little nvh over the heim ends, but it's pretty minimal.