My most successful make was when I used whey from a citric acid mozzarella. I assume that one was better because 1. I added a lot of cream to it once it started to caramelize and 2. it still had all the lactose. I also put it in a blender as recommended to reduce crystallization. That one did taste like Floetemyost
http://www.tine.no/produkter/ost/brunost/tine-fl%C3%B8temysost from the store. Ekte geitost
http://www.tine.no/produkter/ost/brunost/tine-ekte-geitost, or "real goat cheese" is always going to be more tangy than a cow's whey cheese.
My biggest challenge has always been the texture--it should be pretty smooth, creamy, and melt in your mouth. Mine more often than not have crystallized. The flavor is still right (I've done it with whey from a number of different cheeses and haven't noticed a huge difference in flavor, though the one I mentioned above was the best), but the texture is frustrating.
It would make sense that if you want a less tangy flavor, the whey needs to have as little acid in it as possible.