Each race has its own Tech 2 Point defense. A T2 PD has significantly more fire-power then its little T1 brother and most of them will often one-shot most T1 units. The firing range is quite large opposed to its vision so most players will try to make sure to have some radar nearby for optimal efficiency.
A common strategy is to place a couple of T2 point defenses, backed up by a shield, a couple of tactical missile defenses, some AA and a T1 Radar Installation. This makes for a strong defense point that will stop large T1/T2 armies in its path, which can come in handy when you find yourself pushed back early in the game and need to hold a strategic choke point (i.e. in Fields of Isis).
The Aeon T2 Point Defense has a very high single shot damage with a low rate of fire. This means that it has the same DPS as the Aeon T1 Point Defense, making it the T2 point defense with the highest DPS, although it does have a far greater range. This makes it ideal for killing larger targets, and a very poor choice for killing large amounts of smaller ones. The Aeon Point Defense has a blast radius.
The Seraphim T2 Point Defense mirrors the Aeon one in almost every way. It has more health, but no damage radius, but also does 33.3% less damage than the aeon one does, making it a lot less effective at battling more heavily armored units. As it's a beam, it does damage over time - causing it to act quite differently to a projectile - meaning that if it kills a unit before the Damage over Time (DoT) ends, it can move onto another one.
The UEF T2 Point Defense has a lower DPS than the T1 Point Defense (and so, lower than the Aeon and Seraphim T2 PDs), again with a longer range than the T1 PD, typically making it more effective. It fires a salvo of three shots, and has a damage radius - making it good at handling large numbers of units, unlike the Aeon, and generally better than the Seraphim T2 PDs. It has marginally more health than other T2 PDs.
The Cybran T2 Point Defense has a very low DPS for a T2 PD, but again, using a beam, with all of the pros and cons of it (continuous targeting, but with terrain getting in the way more easily). Typically, it is good for the early and mid game, but does not do enough damage to counter late-game units.