I am honestly having a hard time choosing between Tellius and Elibe.
Etrurian emperor has already excellently explained Tellius.
Elibe's variety has certainly been highlighted, but I also love it's lore; The Scouring, The Eight Legends who rose up, and the dramatic clash that resulted in the Ending Winter.
How you can see the Eight Legends' impact on the world through the countries they founded or the regions they resided, and in turn see a lot about the Legends.
I also love the little neat hidden places like hidden town of Arcadia where both dragons and humans live in harmony,
or the Dread Island Valor where Bramimond once called home. Then on Valor there's the Dragon's Gate, the doorway to a whole other world. (It would be really neat to see it someday)
Tellius also has neat lore, but overall I find that Elibe's lore has a flavor I prefer.
That said though, I didn't know Tellius had a lore book, I really can't rank anything till I read that. XD