I love this series a LOT, and I do prefer the manga over the anime, but the anime has its fabulous moments, too. The crossover CLAMP universe characters are so neat and I just enjoy the stories and characters. Quite a few of the chapters touched my heart.
I have a fondness for Kurogane. :ph43r: Or just ninjas in general XD
I adore the series as well -- however, the anime just does not live up to the manga (TOO many fillers and random stories).
Mokona by far is my favorite -- I think I have an unnatural obsession with cute and bubbly types of characters... And of course I adore Fai. CLAMP really is creative when it comes to story ideas~