Neither is exactly a sign of pleasure, but hisses and growls don’t communicate quite the same thing. Basically, a hiss is a sign of fear. Something in the vicinity has really rattled the cat, who hisses at it and, if pressed, will attack but, more likely, will try to flee.
A growl is more of a sign of anger and aggression than of fear. If you’ve ever witnessed a serious cat fight, you’ll hear both cats loudly growling throughout the whole ordeal.