For regular old unit tests I tend to not rely on a framework. I have a single helper class in my tests, URLStubbing that basically fits all my limited needs.
I have used OHHTTPStubs in the past IIRC, but these days I find that I use so little functionality besides a rudimentary implementation of URLProtocol that I think adding another dependency for it is overkill. URLStubbing is not even 160 lines long and includes a lot of documentation about how to use it I wrote for a junior dev I taught.
However, I want to point to Telegraph in this context. I use that for UI tests to mock responses for any requests my app sends out. It's basically a small webserver that runs inside the test runner. A couple of years ago I checked several similar libraries and this one fit that use-case best.
It's not directly a network mocking or stubbing framework, but I think it's close enough to the topic and perhaps useful for people relying on them for unit tests, too.