Yes, I like the very specific answers so far. Let's put team needs aside, and try to put this in a vacuum as best we can.
A team needs to both score goals and prevent goals in order to win a hockey game. So, now we have to make a philosophical assumption and answer the following question. Is it more valuable to score a goal, or to prevent a goal? I think, in simplest terms, it is slightly more valuable to score a goal, and one of the reasons is that you cannot win a game with a score of zero-zero. The winner has to score.
But, like anything else, there is no black-and-white but instead a massive area with different shades of grey. No player is a 100 at scoring goals and a zero at stopping goals, and likewise no player is a zero at scoring goals and a 100 at stopping goals - not even a goalie. You still have to assess each pair on their own: Langway or Gartner? Messier or Bourque? Jimmy Watson or Jimmy Carson?
In the end, after going in circles chasing my tail, I don't think a value can be arbitrarily assigned. For me, it would still come down to some kind of an inwardly biased preference where sometimes I'd take the more defensive guy, and sometimes I'd take the more offensive guy.