I'd go with the HPS. I had the HP+ and aside from the noise (lots) and dust (lots) they were great, with a couple of notes worthy of mention.
They've got a lot of initial bite, which some people don't like, but it worked for me. My car has a lot of pedal travel and the brakes are easy to modulate, so it was a good fit for it (the car) and me (the driver).
They suck when they're cold. When ambient temps are below ~50 degrees, you have to drag the brakes heavily on your way to the start line for your first run. I do it even in 70 degree weather. Hell, in the winter I used to drag the brakes for the 40 yards from my driveway to the first stop sign in the mornings so I'd actually have the ability to stop. Okay, I'm exaggerating a little but they still suck when they're cold.
Bottom line is I think they're great autocross pads, they just require some attentiveness. They suck on the street compared to a street pad; HPS (or similar... even stock) is probably the way to go, and will work fine for autocrossing duty.
Mississippi Region #83 SS / #97 STU