I don’t write primarily in markdown because the format is nice but because markdown apps like Ulysses and Byword value the joy of writing as well as the need for structure. They recognise that writing is equal parts emotional and executive reasoning. Favour emotional logic too much and you get Apple’s glossy, wrapped-in-plastic writing experience. Favour executive reasoning too much and you get Microsoft Office’s kitchen-sink-included helicarrier.
I do all of my writing in Ulysses, and it’s a joy – full Markdown support, with one or two extra touches1 that make everything easy.
As to the Pages vs. Word debate, I tend to use Word – Pages is distinctly easier to use, but it lacks a couple features that I need whenever I’m using a ‘full’ word processor.2