I know everybody has their favorites, but I'd like this topic to be a place to discuss, using logical arguments, which books have the best creativity factors, which has the most developed characters, and similar stuff.
For example, my favorite book is Mistborn, the Hero of Ages. By this time in the series, most of the characters are all very well developed. In this book some characters we'd wanted to know more about (Spook and Goradel) have their moments and we finally get to see how they affect the world around them and how they face the growing threat by Ruin and the koloss.
The worldbuilding in Mistborn amazed me, especially the prospects of the ever-falling ash and the Shards' affects on the world (hemalurgy and allomancy).
I loved the intricate magic systems and the setting of the series: what if the Dark Lord won? Most of all, I loved the ending of HoA, where all the connections connected and revelations abounded.
Overall, this is not only my favorite Sanderson book, but most likely my favorite book of all time, at the level of works such as J.R.R. Tolkien.