When comparing MarkdownPad vs Marktext, the Slant community recommends MarkdownPad for most people. In the question“What are the best open source Markdown editors for UNIX-like systems?” MarkdownPad is ranked 36th while Marktext is ranked 38th. The most important reason people chose MarkdownPad is:
A custom CSS can be added to the rendered HTML to change the preview and output.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Allows customizing output
A custom CSS can be added to the rendered HTML to change the preview and output.

Pro Real-time HTML Preview
MarkdownPad is split in two panes. One pane is used for writing Markdown, the other shows the rendered HTML as it's written.
Pro Copy Paste keeps formatting
Copy pasting from web and other sources keeps formatting, which is great time saver.
Pro Output HTML and PDF files
Pro Various editing modes
Source Code mode, Typewriter mode, Focus mode.
Pro Various themes
Pro Paragraphs and inline style shortcuts
Pro Math expressions (KaTeX
Pro selective support Pandoc markdown
Pro GitHub Flavored Markdown Spec
Pro Support CommonMark Spec
Pro Realtime preview (WYSIWYG)
Pro Cross Platform
Windows, Mac , Linux
Pro Open Source
Cons

Con Many features are disabled in the free version
Free version lacks features like auto-save, PDF export, Markdown tables among many others and can't be used commercially.
Con Abandoned project
Nothing from author since 03/15. Pro version preview pane crashes, no fix has been offered. See user forums.
Con Preview window crashes / does not update
