I think the Heavy PPC is better for IS v IS games. You want to get in close usually for your other guns, so the reduced range isnt that big of a deal--you do your best damage with IS mechs up close, and they tend to be slower so the worse brackets and minimum range are less deal breakers. Melee tends to suffer with the HPPC min range, but IS melee mechs usually rock heat penalties from TSM and dont count on their weapons at all when the fists start flying.
For IS v Clan games, the ER PPC. If a Dasher runs up behind you, and you point an HPPC at it, you are likely gonna miss when you cant afford to. Likewise, if they bring lots of fast or long ranged things, the ER PPCs trade well compared to the other weapons. An ERPPC versus a HPPC targeting something at 7 hexes for example, with a 2-3 TMM, like a Vulture? The HPPC is on the 8+ side of the bell curve, so it diminishes greatly, while the ER PPC on 6s is putting solid hits into that Vulture the clan player cant afford on such an expensive frame. With so many clan weapons having longer base range + speed advantages, the ERPPC plus a brick of armor is a good counter.