That's a tough one. I am trying to trade Rask myself right now but I don't think I'd trade him for Halak. As you said, there is the injury history plus he is clearly not as good as Rask.
Now it would help to know your league's goalie cats? If it's wins-heavy, then I'd probably take Halak still but if it counts other stats like SV% and GAA and S, I'd want more for Rask.