Depends on what type of mage you are.
Caster mage- The focus of the mystic for more focus for harder hits and more energy/regen (because casters almost always run out

)
Dps/melee mage- Any offhand weapon that you like, I coordinate it with my lure, so fire dagger or fire blade etc. Considering the dragon mage weapon seems to be geared towards melee, this build may be a better fit for some people. Can also use less energy with a fire melee build.
Self-preservation solo mage- Shield of the bastion. I used this for hard bosses at start of update, but unless you solo a lot I don't know that it would be worth the investment. With an optimal boss/lvling group, higher vit build, and maxed eshield (I have 3k vit and maxed eshield, however I am primarily support at the moment and this might not work for a higher energy usage caster dps build), I don't need the shield anymore.
The reason I (still) love my mage is that you can change your build, I don't believe you are relegated to one role (the people angry about the mage nerf will probably disagree), so you can have multiple useful offhands that fit the role you choose to use.
Hope this helps!
