From my knowledge, an x pipe is better in the fact that it allows the exhaust pulses (from cylinders) to follow each other and create "momentum" (pushing and pulling pressures) therefor creating better flow. Obviously deleting the resonator will provide more sound. As far as I know, an H pipe is really only to equalize pressure and allow more free-flow but not efficiently. Then again, this is coming from research I did over a year ago so I could be incorrect.