In ePub you get 5 fonts sizes and a landscape mode option. This is a new capability for the Hanlins, with a few rough edges that will likely be sorted out soon. It is already my favorite format for the Pocket Pro.
In MOBI you get 3 font sizes all in portrait mode, but you can add your own fonts (see
I Love my first eReader, a Pocket Pro 5"). This is the most full featured of the Hanlin's formats.
The other format to try is FB2, which is using a 3rd completely different reader (CoolReader). It has 5 font sizes and landscape. This should also allow user-provided fonts, although I could not get this to work (as it does on my EZ Reader Basic). This isn't a common format in the upload section, but Calibre can convert many DRM-free formats to FB2.
I consider LIT and CHM to be un-usable on the Hanlins.
The TXT-like formats, TXT, PalmDOC, HTML, RTF, DOC, etcetera use a set of related readers which are OK but not as good as the ePub, MOBI, FB2 readers.