I prefer to mock below the level of the 3rd party client library. In rubyland we use VCR to stub out the lower level network libraries to record the requests/responses. Then during the test runs your network libraries don't make real connections to the APIs - they just play back the recorded responses.

Python has ports of VCR (betamax and VCR.py).

The benefits of this are numerous. You don't need to manually build and verify mocks. You don't need to build a facade for every api client (the api client is already a facade). You exercise the as much of the 3rd party library code as possible on each test - this is very helpful during library upgrades. You can verify your recordings by switching your test to "live" mode every now and then (just configure your CI env do that every day or every week).