I read book one like, twelve years ago, and there were only two things I could really remember from the book, after watching the show. I have just read the book again after watching the show, and I honestly do not remember any of it being the way it is. I mean the tone and the feel are nothing like I remember.
I couldn't say which I find better. Usually, I think whichever medium I encounter first is superior. Thats why I think the film fight club is better than the book, and why Captain Corelli's Mandolin is a better book than the movie (though I doubt I'd think the other way around in that circumstance)
I was very surprised with just how faithful the first season was to the book, for 90% of it anyway. Yes, some of it was comressed for budget/time reasons, but even so. And the stuff they added I thought was fantastic (The two scenes between Varys and Littlefinger for example, and pretty much any scene with Doreah in it. God damn does she play that role well)
Since I'm in the UK and dont watch TV, I'll have to wait for the season 2 bluray next year, so it'll be a while, but the changes they made towards the end of season one were kinda major (surrounding the battle at the end) and that deviation is going to have a massive knock on effect, from what I've read of the second book already.
So I think I'm going to say that they are equally good at what they do. The show is one of the highest quality productions I've ever seen on TV (but then again, so was the first season of Carnivale, and look how badly that went) and the books are - considering their size and density - extremely easy reading.