If I had to choose, my favorite website would be the High School DxD Fandom Wiki. This site is no more than just a fan-made wiki for a great anime called High School DxD. A little background on the anime:
Issei Hyoudou, the protagonist, transfers to an all girls school that just became co-ed in hopes of becoming popular and having a harem. Dispite his dreams he is killed and resurrected by the top idol of the school, Rias Gremory, as a demon and her servant. He must then risk his life for whatever she desires.
I like this website mainly for its anime theme and info that people like me can recieve, such as a character's birthdate, or even background information on a character that it doesn't give you in the anime, but rather the light novel or manga. This is exactly what the site is for, to give information to the user about High School DxD. What I specifically like about the site is it's easy to understand navigation. If I could change one thing though, it would be their background. They have a picture for it and it's great, but it is tiled and doesn't have a smooth look.