I've been using stock Touchwiz launcher since I got my S4, but I had purchased Nova Prime a while ago. Finally decided to switch and I'm LOVING it. There are a few annoyances with stock Touchwiz, but Nova fixes all of them. In Nova you can change icons, change desktop grid size, and configure it so that long pressing the menu button launches Google Now, which I prefer. Also, Nova takes up MUCH less memory than Touchwiz. In Ram Manager, with Touchwiz, I was always hovering around 1.3 gb - since using Nova I've been hovering around 1.00 gb. Thats a lot less memory being eaten up.
Nova also lets me use almost all of the Touchwiz widgets. The only one I've seen that it really won't allow is the weather widget. S Health, Alarm, Music, S Memo, S Bookmarks - all are able to be used in Nova. Nova also lets you use a transparent notification bar, which I really did like on Touchwiz.