They both suck, that's why I play a Swordmage. 
Look at it this way: A defender's role is not to negate damage, but to minimize cumulative damage. This can be done a number of ways.
1. Take the attack instead of squishier cohort.
2. Block the enemy from getting to the back.
3. Negate damage taken either by Aegis or healing.
4. Damage said baddie more and kill them quicker, there by negating attacks.
5. Nerf baddie's attacks.
6.........etc...........
There's more than one way to eat an apple and there's more than one way to be a good defender.

Look at it this way: A defender's role is not to negate damage, but to minimize cumulative damage. This can be done a number of ways.
1. Take the attack instead of squishier cohort.
2. Block the enemy from getting to the back.
3. Negate damage taken either by Aegis or healing.
4. Damage said baddie more and kill them quicker, there by negating attacks.
5. Nerf baddie's attacks.
6.........etc...........
There's more than one way to eat an apple and there's more than one way to be a good defender.