I preferred
Volkhov at first, but I've now settled for
Arvo. Both are great. Arvo is similar to Caecilia in the Kindle app.
I should add I use Marvin almost exclusively in Night Mode ("
Fulvous" text colour on pitch-
black background at about 75% brightness), because I prefer reading on hardware e-ink Kindles (especially Kindle DX) in daytime.
In Stanza, I preferred the very nice
Futura for Night Mode, and
Georgia for Day Mode. (Both are also available in Marvin.)
The great thing about Arvo is that it seems equally suitable for Night Mode and Day Mode. And that's quite an achievement, because serif fonts usually look bad (too indistinct) in Night Mode. Not Arvo!
I also read Russian e-books in Marvin, and for them, unfortunately, none of the fonts Marvin promotes at the top of the fonts list is available. So, for Russian texts, I need to go to
Verdana. Verdana is a fine font, but so ubiquitous it seems slightly boring.
I do prefer Verdana for
headings in all situations, though, so my preferred Marvin combination is Arvo for text, Verdana for headings.