A little over halfway through the book now. Interestingly enough, I find Daenerys' chapters to be the most boring (considering how integral she is to this book in particular). The politics within her campaign just aren't as engrossing as those in Westeros, so I find oftentimes her storyline more plodding than anything.
I really love Reek's chapters and whatever chapters Stannis is in, however. I've always had a soft spot for Stannis. I forget who says it, but after reflecting on all the candidates for the throne he or she closes it with Stannis, saying something like, "...and everyone hates Stannis." It's true, and that's why I find him both hilarious and absolutely intriguing.
Bran's chapters are quite good as well.
And, of course, Tyrion's chapters are always engrossing no matter what.