Both are important. I can't say they're equal either though. Thus, I'll have a zen moment and say both are important and different.
The old adage expose for the shadows and develop for the highlights works here. I've always thought that the goal was to get all the information possible on the sheet of film. Thus, we expose the film getting enough exposure to produce the desired details in the shadows. As Ole mentioned a little overexposre will guarantee that we get the shadow detail. However, too much overexposure will shove the highlights onto the shoulder. Flat highlights isn't any good either. However, we can control this with the proper film, developer, and development choice.
So, this is why many people encourage testing of film, paper, etc. IMHO, two of the best darkroom tools I have are my densitometer and my stouffer density wedge.
In conclusion, both are important. However, knowing how your materials respond is most important.