I would probably go with the THDP - ive never heard a complaint about their DP..... and this from someone who HAS an ATR DP.... which i have to remove and send back because the puck sticks HTH
I had a Houston style ATR downpipe I bought used. It worked well for a while, but then the puck started sticking. Many others had this problem with the ATR DP. I haven't really heard of any problems from the guys running THDP's.