A) The manga version cuts some minor scenes, particularly some banter. The banter is the best part about this series, so you don't want to miss out on that. There are also some altered scenes from the LN/anime (such as Mai's blushing)
B) The manga version is more expensive. $24 retail, versus the Light Novel which is $15 retail.
C) The Light Novel is significantly farther ahead in the story. The manga version only goes up to the Futaba arc currently (3 volumes).
D) And finally the manga has waaaaaay too much fan service (Mai image in shower, Futaba's exaggerated breasts, Tomoe panty shot, Mai's bunny suit is exceedingly tight around her body, etc). That really hurts what is otherwise a fantastic story. I have heard that the next arc has a lot less fan service. But this is a review of the first manga volume that I read- Mai's arc.
The art is pretty good. But otherwise, the only reason to get this is if you want a fan-service version of Bunny Girl Senpai.
Watch the anime and read the light novels. This series has a lot of great characters, wholesome and heartwarming romance, realistic drama, and comedy. Highly recommended series to all fans of those things...for the Light Novel and anime versions, anyway.
