the manga is far superior to the anime for two simple reasons
- It doesn't have that annoying brat Winner in it
- The story is WAY longer. The anime was made before all 14 volumes were completed, thus it lacks key plot point such as why Karin has her blood increase
The manga has been completed now, tallying 14 volumes in total. A must read. There's also light novels, but only 5 of them have been translated into english >_<