In most games, more def > more HP always.
Um, what? Maybe I'm playing in bizarro world, but it's pretty much always the other way around in what I play. Basic instinct would make you think more def = less damage taken = less healing = less need for higher max HP, etc, but by the time you start seeing a real difference in damage, something else like a multiplier determined by relative levels of attacker/attackee is also in play.
Then there's the fact that HP pads you no matter what you're getting hit by, rather than just playing a role if it's a physical or special/magical attack.