The 1 heat per point of damage is identical. The PPC takes up one more critical slot (50% more) and 2 more tons (40% more) in order to boost the damage (+25%) and shift the range band out by 3 hexes (+20%), leaving a weak area in the 3 closest hexes instead of 3 hexes where it simply can't reach. All in all, I'd say the choice depends on the function of the 'Mech.
If I'm planning on closing into brawling range, and have the speed to do so, then I probably want the LL's infighting capability, unless I've already got a battery of MLs or SRMs to cover that, and don't have the heat dissipation to use both. If I don't have the speed to close, or do, but would prefer to remain at longer range, then the PPC allows me to fight from that greater distance. The PPC is more effective in a "bracket fire" design, while the LL excels in an "alpha strike" design.
There's no clear answer between the two, and I can easily see examples where one or the other would be the better option under the circumstances. In my opinion, the ML is "King", and both the PPC and LL are merely somewhat dissimilar Lords under his mighty banner.