A Game of Thrones
Best: Daenerys - Love her character development and the introduction to Essos.
Worst: Sansa - Most of her storyline is buildup that doesn't receive any payoff until ASOS. Great, but frustrating to read.
A Clash of Kings
Best: Davos - Stannis' storyline is godly.
Worst: Sansa - See AGOT.
A Storm of Swords
Best: Sansa - My god. I went from dreading Sansa chapters to dreading when they ended. Beautifully depicting the death of innocence.
Worst: Samwell - It was good, but quite evidently the weakest in the novel. Aside from the White Walker clash, nothing really of interest.
A Feast for Crows
Best: Jaime - Everything about Jaime's Riverlands arc was fantastic. Almost as good as his time with Brienne.
Worst: Samwell - Again, one or two highlights (Aemon's death, his last chapter), but nothing of great significance.
A Dance With Dragons
Best: Theon - Out of all the superb northern arcs, GRRM's depiction of a broken man attempting to heal is his most poignant arc ever.
Worst: Quentyn - For someone who enjoys Arianne's POV, her brother is an absolute bore.
Despite not being on this list, Jon and Arya are probably the most consistently enjoyable POVs for me overall.