1. Tyrions Wife, Tysha
The Show Everyone better remember this, because as any book reader will tell you its crucial to Tyrions character. In the first season, the night before battle, Tyrion got drunk and spilled his sad story. He and his brother had rescued a girl named Tysha from rapists. He took her to an inn and bought her food. Then they went upstairs and he lost his virginity. Within a few days they were married, and for a while they lived in Tyshas house (hiding from his father). Then Jaime and Tywin came to get him, and Jaime told him that Tysha was a whore the whole time, hired by Jaime to deflower Tyrion. To demonstrate this, Tywin hired Tysha to service his entire guard while Tyrion watched, giving her a silver coin for each man. By the end she had so many coins that they were slipping through her fingers. The Book It played out much the same, although Tyrion was only talking to Bron and it wasnt the night before a battle. There was one crucial difference: after Tysha had serviced all the guards, Tywin decided that Tyrion would fuck her too, and pay with gold because a Lannister is worth a gold coin.
Verdict: The Book This one was worse in the book because its more important in the book. Im not sure if Tyrion ever visits a whore in the novels without thinking of Tysha. He hallucinates her, he dreams of her, he projects her onto Shae (who as a result never has an individual character). And the last little twist of the knife that is the gold Lannister coin makes the book far more brutal.
Honorable Mention: Jon Leaving Ygritte
The Show Jon decides he cannot kill an unarmed man, even if it means dying. He stops Ygritte from helping him and breaking forever with her people, then runs away leaving her behind. He and Ygritte had been in love, and she believed he would never leave her. Its probably the one thing he could do that, to her, qualified as unforgivable. The Book He also leaves to avoid killing an unarmed old man. But Ygritte shouts Im no crow wife and slits the guys throat. Then Jon has to run while Ygritte gives him a parting gift of an arrow to the leg. They werent quite so close in the books.
Verdict: The Show Ygrittes understanding of their relationship is shattered in the show. In the books, their liaison is more casual, and thus easier to end. It's just a question of impact, and in the book there's little impact on the characters or the reader from Ygritte and Jon's break-up.