I read books and prefer them to show (except Dance of Dragons).
Books is full of sex and violence because Westeros is like ancient England (seven reigns, Wall... Robin Hood!) and this is very good, realistic, but tv show take out many important thing for prefer and invent sexual scene without sense. I love Martin's books, "Wild cards" too, but tv show is by HBO: they turn a great fantasy in Sex and the City with swords and the tv- fan like twilighter (so, here in Italy is that: it's seem they don't even see a book!)
The books for sure, I think they've taken too many liberties with the tv show and have watered down the characters I like because of the liberties that they've taken. For example Arya, she's too much like a little girl in the show instead of the fierce person she is in the book.