I had a prochamber, loved it. Youll keep more bottom end with the Prochamber, but it wont be as loud as just a plain H pipe. Still loved the sound and power it gave me though.
Prochamber hands down for sound and performance. If you want louder, go with H. For tone, go with Prochamber.
+1 althought a I met a guy with a prochamber and dumps and it was pretty loud and "racey". My H still sounded better though.