is it better to have more cores or more ghz in a processor?
That all entirely depends on several factors.
A fast dual core will outrun a slow quad. Different generations of chips cannot be compared using GHz anymore, as newer chips do more with less (AMD has always done this which is why Intel was always pushing GHz).
Basically, your proposed usage (gaming vs encoding or multi-threading) and the generations of the chips being compared will be what will decide the question.