I have my favorite reading fonts. I do not like Caecilia at all. It reminds me of old west style writing not something I want to read every book with. I prefer Sans-Serif but I currently use a Serif font.
I use
Amasis Modified. It basically Amasis that has been edited to look better on eInk. Someone here edited and it has saved me from dealing with font and contrast unhappiness
On my Tablet I use Amasis Modified or Trebuchet before that It was Tahoma. On my old eReader which was before Pearl I used TheSans.
I have tried many fonts but I always go back to those three.