There really isn't a debate to this. The 4790k is simply better in all regards. It is not like a situation where one is a 4 core CPU with higher clocks than a 6 core CPU. Here, both are 4 cores, each on the same architecture, and the 4790k has a higher clock rate. Therefore, it is technically better.
However, as far as just general gaming purposes go, the 4770k is more than enough and you won't likely see any significant increase in performance between the two. If you can find the 4770k for a significantly lower price than the 4790k, it will certainly be good enough. However, keep in mind that the 4790k is priced the same as the 4770k was when it was released, so if the prices are off by a measly 20 dollars or so, you might as well go for the 4790k.