There's two arguments on this one - take light, and be a faster, more agile tank, or take cold, and be a slower, better defended tank.
Either way, you're still a tank.
I'd say you'll spend the majority of your time running from mob to mob to kill stuff, so take the speed bonus. You'll be fine through the 100 cap with heuksal/fire/light trees. At that point you'll have to start thinking about keeping speed, or delvling for more fire.
And definitely get the spear toss moves - you'll have 3 books of those eventually. They bring the mobs to you and speed grinding up a lot.
GL, happy grinding.
