I use both regularly — markdown / dual-mode and rich text / WYSIWYG — in different settings.
My ideal solution is embodied in the writing app Ulysses. It combines markdown and styling in a beautiful, intuitive, seamless, single-mode way.
Technically they do have another mode. Markdown-less rendering is available but they've pushed it out to the final presentation, where you can export to any one of numerous available styles when creating a final PDF / HTML / Word / etc. document. That decision works well for me; what they offer in their editing mode is perfect, until I'm finished and need to share / present to others.
At least check it out as an option if you haven't. It's the best implementation of single mode markdown I've seen.