Magicka DK in pvp... get ready for the tears. To answer your question I would take the heal. That is unless you're going to back bar resto. GDB for a heal is lackluster.
For pvp the problem you will encounter is that as a dot based build, your dots won't stay up. They will be cleansed off and you have zero burst.
You could try armaments with heavy attack but it's dodgable. And slow..
If you want to pvp on your DK the consensus will be to roll Stam. I have a Magicka dk and love him, but purely from a pve standpoint.
Regarding chains, they are bugged. If you are not on level ground it is unreliable. But at least you have flappy wings right.