Thinking of exhaust mod

If it's a fair amount cheaper then go with the H-pipe but if the price is right there's no reason not to go with an X-pipe. The sound will decrease a bit but a swap to louder mufflers will help that. Look at modern V8-powered cars, not a single one has "true" duals or even an H-pipe; all of them that have dual exhaust have an X-pipe crossover. Also, the ideal place is supposed to be calculated with the exhaust you have and on most systems is a few inches behind the transmission pan (mostly for easy access to the tranny) but that may not be ideal depending on the engine/header combo.