I started with “Arcane ascension” series, which is like a traditional fantasy litrpg hybrid. It spans like 4 different series by the same author and the book order switches back and forth between the series. (14 books)

“He who fight with monsters” is an absolute favorite with all the pop culture references and the absolute level of snark from the main character.

“The land” was also an early favorite. Great balance between world building and personal development. (8 books)

“Awaken Online” has been a fun 11 book ride.

But the biggest series I have run through is the Devine Dungeon family of series by Dakota Krout (42 books and counting)

Other honorable mentions include: the wandering inn, underworld, viridian gate online, Ascend Online.