I agree in the way that Jon and Ygritte are more developed on screen. The majority of the scenes between them in the show are adapted from the book but they are quite a lot of added scenes (almost all their scenes in season 2, Ygritte’s funeral, the climb that is way more romanticized and revolve about Jon and Ygritte more than it does in the book, or even Jon watching Ygritte being killed) and as you spend more time with them watching the show than reading the book, you can think that they are “better” on screen. As a fan I’m really really glad they spent time developing their relationship because it’s such an important and beautiful one (and my favourite). It really went beyond my expectations and hopes and they really did a good job with this storyline.
However Jon and Ygritte in the show aren’t quite Jon and Ygritte in the book. Jon is less of a lost puppy in the book and there are no rivalry with Orell ; on the contrary he’s trying hard to not be friends with the wildlings because he appreciates them after he realizes that they’re just people (different people, but people all the same) and not monsters or something. As for Ygritte, she’s way softer in the show. Jon says of her that she’s “wildling to the bone” and that’s why there’s a dimension of her he can’t quite understand. Ygritte didn’t want to hug Jon after they almost fell from the wall because she was not scared of falling but of the wall itself and he didn’t understand that ; I’m not sure she would have spared a mother and a baby ; she didn’t come crying after Jon when he ran away but put an arrow straight the moment he started running towards a horse to come back to Castle Black. The creators of the show made also a bold decision by replacing the time Jon spends with Qhorin Halfhand in the second book with time bickering with Ygritte. A lot of people aren’t pleased by that and I understand them even though I’m obviously happy they took that path (I would have loved more time with Qhorin especially considering how good was the actor but we can’t have it all I guess). They did it in order to develop Jon and Ygritte’s relationship from the start and their scenes in the second series are among their best ones but it’s true that if you are fond of the scenes between Jon and Qhorin (which are really interesting and so important for Jon, he thinks about Qhorin’s words all the time) you may find Jon/Ygritte and Ygritte more annoying than in the book.
So if you look past that, the fact that their characters are a bit different and their relationship being more “romantic”, you could say that Jon/Ygritte is a better thing in the show than in the book. To be honest I don’t think I really have an opinion about it because I love both versions. The majority of the quotes I love about them (especially the quiet time they have at Queenscrown and all the time they talk about castles) are in the books only but they are really well portrayed in the show so I really like both but not in the same way/for the same reasons. :)