This is what I understand about this subject:
H-pipes give lower RPM a really muscle car sound, X-pipe will quiet the amount of drone in the cabin and change sound some at higher RPM's, and straight pipes are straight pipes. I'm going with X-Pipe after next paycheck comes in.
I have also heard that X-pipes add some power, but i don't think it'll ever be enough to make a noticeable difference.
Thanks Guys. I had the flowmasters 40 series installed with straight pipe. I think before it had glass packs on it at least thats what they looked like. It's not as loud as it was before, but definitely feels like its performing better. Maybe I'll upgrade to an H or X pipe later down the line....