The feature I really like is the preview function, being able to see what the post will look like.
This is where I ran into an issue with Thesis, I had pretty much left the settings to the defaults as far as font size etc… I did however change the font to use Arial. When viewing the preview in Marsedit with the Thesis theme, it would not display correctly.
The theme’s body was only about 80 percent of the width of the header graphic. I spent a few hours chasing CSS etc… trying to fix this display issue. I was finally able to solve it within Marsedit by changing the font size.
The font size in Thesis was set to Arial 1.4em, setting the Marsedit main preferences to Arial 16px fixed the preview display issues with the WordPress theme.
Of course changing the default font size also meant that my Drupal sites would not display correctly in the preview mode.
After a while of playing with the CSS for the Drupal sites, I arrived at a happy combination that finally displayed My Drupal sites preview almost perfect and my Thesis blogs as well.
I think using an external editor is the best way to go, especially if you’re using WordPress with its incessant pinging. While there are many different versions and manufactures of this software, if you’re a Mac user in my opinion Marsedit is the best.