If you are building a large application and don't have a team that are all really good at writing decoupled code that can be well-tested with black box tests and are prepared to fully embrace using/debugging lots of mocks & stubs, don't go down the Factory road.
Wherever you read about how Awesome Factories Are you'll see a little caveat about how factories might not be feasible in a large application because they are a little slower than fixtures.
But "a little slower" is really orders of magnitude slower.
Factories are not significantly easier to code than fixtures that use labels for ids, so long as you keep the fixtures organized. And in some cases factories are harder to debug.
Just tonight I converted a single factory to fixtures, and the runtime of the test file that used it went from 65 seconds to 15 seconds, even though only about 15% of the tests in that test file use that factory.
If you use minitest you can run your tests in random order; this will quickly reveal any data coupling between tests. (not sure if rspec has the option to randomize test order)