X or H cross.

I raised this very same question to my custom exhaust guy just before he made my H pipe duals up. My nephew has worked for him for a few years off and on while going to school and he's got a fantastic reputation in the New England area. His name is Dave and his shop is called Skip's custon exhaust, located in Southern N.H.
He advised that both designs offer equalization of back pressure but the x design is best for circle track racing. Wish I had asked him why.
My exhaust exits full tube headers to a 2 1/2 with H design, through thrush turbo's. Sound throaty as all get out. I Love it.