Depends on your ships heat ratio, if your ship tends to overheat easily, then "Thermal Vent" is best. My Corvette has all beams, cept for the 2 huge MCs, the 3 largest ports the beams are efficient with healing beams, the 2 smallest ports are both efficient with "Thermal Vent", with 3.5 pips to wpns, can fire sustained all 5 beams for 45 seconds, or longer if the underbelly beam isn't firing cause the target is above you, with 4 pips to wpns, my engineered PD keeps pace with the juice required and can fire without letting up. Now, firing all weapons, the MCs included, runs outta juice in bout 20 seconds, but doesn't matter cause by that time the target is toast anyhow, regardless what I'm firing out. In CZs, I can burn through a Corvettes shields in under a minute, unless its a cheater NPC that spams shield cells, but once his shields are down, its about 10 rounds of the huge MCs into the PP and its is a sitting duck. For the cheater NPCs, I like to do a boost ram to overcome his "cheat." Thermal Vent takes heat away from your ship if your beams are connecting, of course, it loses the effect if you are missing the target. Some ships run hotter than others, so if you go with beams, efficient with thermal vents will keep it from overheating. On my Corvette, the only time it gets close to heating up is when I am firing every weapon at the same time, but even then it does not overheat.