There is a poll also in this forum that has the very same discussion ongoing:
Poll: What writing software do you use?
My preference is PowerWriter (Win only) and yWriter (Win & Linux):
like PowerWriter because it organizes writing tools closest to the way I think. I like the blank page in the largest part of the window, a tree view of the book, acts, chapters and scenes in the left pane, and multiple tabs for the writer's paraphenalia across the bottom of the window. It has a good number of prep tools (Premise, Synopsis, Characters, Plot Points, and Notes/Research). A useful feature is the ability to embed notes (e.g. "come back to this paragraph and write a long description about what the protagonist was feeling..."). I paid $100 for PowerWriter three years ago and there hasn't been a major upgrade but several small updates. Very stable and the only reason I keep looking elsewhere is that it stores all data in a PowerWriter database. It will auto-backup to another drive which I do, but as nervous as I am about losing my drivel, I still output an RTF file about once a week so that if PowerWriter never works again, I could move my work to about any other program.
You can't beat yWriter for value though since it is Free (Donations recommended since the author of yWriter is a Sci-Fi writer that uses it to write and publish his works, and improves yWriter along the way). Very full-featured and if it displayed the blank page while showing all the tabs for charaters, locations, items, etc., it would be my only creative writing tool. Truthfully, I sent Simon a small donation last year because I used yWriter during NaNoWriMo which was long enough to know it just doesn't fit me as well as PowerWriter does. simon keeps improving it (now version 5 and each was a major upgrade with small updates in between) and I keep downloading the updates and testing what he's changed about once a month. At some point he'll add enough features, or the features that fit me, and it will supplant my old PowerWriter fav. I look forward to this for one big reason: Simon uses RFT files as the individual documents to park data in this program, not a proprietary database. To me that's pretty big and if the Scene editor just acted a little more like a word processor, it would be the perfect tool for me. Many folks, including several puplished authors use it as their primary tool.