The three formats that are worth comparing are FB2, ePub and MOBI. They each use a different viewer on the ECO Reader. Since you are using Stanza, ePub may be simplest.
One issue with ePub is that there are no options on the device except font size and screen orientation. So if you want a Sans Serif font, or bold text, or left justification this needs to be in the ePub. I like all three, so I use the following extra.css (for Calibre, I don't know how to use this with Stanza):
Code:
body {
font-family: sans-serif;
font-weight: bold;
text-align: left;
}
The default is the Serif font, normal weight, and full justification.