Well, the main point is that Manga is the base for the Anime most of the time. Manga usually has more of the information then the Anime, Manga has more style, it is a form of art, and very good art indeed.
It is like compairing a movie and a book, obviously the book is going to be better for the most part.
Anime sometimes alters a few things in the manga.
For example, in the Fruits Basket Manga one of the characters is a female, but in the Anime they turned him male, or vise versa which is kind of freaky to me.
I personally wouldn't want a gender bender in any of the mangas I read. I cannot imagine Cain from Godchild as a female, it just doesn't seam right.
Althought Anime can be better then manga, for example. I am unsure of the name of the manga, but it's drawing style is not very pleasant to the eye...the eyes were a bit out of place and there were a bunch of other things wrong with it...
But I honestly think it would have made a great Anime.
So, you see? It really depends on how you look at it. In some cases Anime is better and in the other cases, it is completely opposite...