The Magician's Tower

AC is like interest, if you arent getting constantly hit, the value of it is hugely deminished. Getting hit once or twice a pull doesn't qualify if your hps can take those hits. AC is best used on tanks because it will lower the average hits over time and make healing tons easier. You really need to be getting hit overtime for lots of rounds for AC to exceed what HPs will do for you. Also, like mentioned before AC has no effect on spell damage. So if a choice, I choose HPs. There are many an aug that have both though, so I wouldn't trade out say 30 AC for like 20 hp gain.