I'd be happier with the fat model version than the fat controller. At least that way is amenable to Using the same code via multiple different user interfaces. For example, the normal web site, a mobile app, a data import, and an admin path, and something else that hasn't been though of yet. In general, designing things as though there will be more user interfaces for it in the future is helpful, and tends to push logic out of the controllers.

I see a lot of unit tests like the ones described in this article and have some doubts about their effectiveness for doing much more than spotting syntax errors. Integration testing is still important if the goal is avoiding defects getting out to production.