Is vocabulary or reading comp more important for GRE verbal?

Work on the area that currently leads to more wrong answers, or where you have a shorter path toward improved performance. That varies from person to person.

For reading comp, you may be able to make gains by improving your strategy and approach, which can lead to relatively quick improvements. Other gains come from bulk practice and require more time.

Similarly, for vocab-based questions, strategy improvements alone may help even before you've studied much vocab. Most people don't see an immediate score improvement from studying vocab — it takes significant time to build enough knowledge to move the needle meaningfully. But if vocab is what's holding you back, it's what you should work on.

If you need gains significant enough to rely on improvements in both areas, most people want to put in enough time to make the easier gains in each first. The question becomes: which one do you continue with longer when the other one stalls out and stops offering good opportunities for improvement?