There is no one "best" jpipe. Different applications will require different needs on exhaust scavenging. What may be best for one setup may prove to be ineffective on another. The RV6 V3 is better for low end because of the super long primaries. The XLR8 V2 outperformed the V1 by 10hp/tq. They haven't been tested back to back. The ATLP V2 was dynod right after the RV6 V3 on the same car and made slightly more power up top, while the RV6 made more down low.