Hi there,
Both of these are excellent gold stocks, have nice growth and both are cheap. Which one you add will likely depend on your risk tolerance. As a streamer FNV is typically less volatile, and the dividend is more reliable. It is the only gold stock that didn't cut the dividend (and in fact raised it) when gold was trading at depressed prices for the better part of the past decade. As a streamer it doesn't have as much capital costs and as such, is more defensive than a producer.
As a producer, KL will likely be more volatile than KL. Will probably yield greater returns in a gold bull market and drop more when the industry struggles.
So which you chose will depend on your risk tolerance. They are not directly comparable because have two very different business models. So you can look at them as less risk = FNV and more risk = KL. Both however, will rise and fall with the broader industry.
Mat