In the real world it boils down to how you use your computer; what software you run and the nature of your "work" environment.
In general, I prefer notebooks up and until I turn them on. At that point I prefer a desktop. When I'm not using my computer, either doing non-computer things or carrying the computer from one place to another, I prefer that it be a notebook so that it consumes little space and/or is easy to carry. Once I turn it on to use it, I prefer a desktop's large monitor, separate keyboard, and mouse instead of clumsy trackpad. With the software I run, I also prefer to have the processor power, large quantity of RAM, and massive harddrives (plural!) that are easy to achieve with a desktop.
Its true that you can attach external monitors, mice, keyboards and multiple external HDDs to a notebook, but few notebooks, no MacBook of any sort, has the guts (processor, RAM, GPU, ...) to match a good desktop. Those few Windows and Linux notebooks that come close are heavy and have only rather modest battery life and serve a market that Apple doesn't try to service.