I actually had both. I like the O/R H-pipe better. The H-pipe is a little louder in volume, deeper, and has more rumble. When I had the pro-chamber the tone was cleaner but a lot quieter compared to the O/R H-pipe. It is not much louder than the stock midpipe. Plus the price of the H-pipe is about half of the pro-chamber. It all depends on your own likings. Everybody is going to have different opinions, but I like the H-pipe better.
I have an off road mac h pipe with original 40 series flowmaster mufflers. I love it , and would not change anything its a good set up. If you like the way old 60's muscle cars sound then you will like an offroad h pipe with flows. X pipes sound too much like a european car to me. x pipes are more raspy too. I hear x pipes flow better but I dont think there is much difference in power between X and h pipes. I would go with an off road h pipe for the classic mustang sound!
I had an off road H on my '91 with Flows and liked the sound. I have the Prochamber and Flows on the Mach and I I like it more that the H. The Prochamber doesn't make it as loud as the H, but the sound is deeper. I hate MAC stuff too, but I'm impressed with the Prochamber.
just bought mac lt's prochamber & magnapack system today. can't wait to get it on car, should be here late this week. I know this will sound sick cause i heard clips and i'm sure the clips don't even do it justice.
I have Super 40 Flows and a ProChamber. The tone outside is just amazing, btw it doesn't sound "off road" at all, no raw tones or rasp just really throaty and mean. It's VERY quiet though and inside it doesn't sound nearly as good, all I hear from inside is a deep "HUMM", doesn't sound aggressive at all. I think i'd get an H pipe even though ive never heard one in person. No problems at all with drone though if thats a concern.