I got Nova Launcher Prime as well and I'm using it as my default launcher right now over Touchwiz and I like it so far with not much difference in speed with TW. I like the scrolling wallpaper effect similar to other launchers like ADW Launcher Ex. There are a lot of settings to try out and they can be very subjective. I do like the card stack scroll effect for the Desktop and Drawer and the Jelly Bean app animation. Most of the TW widgets work on Nova Launcher Prime except for the Clock & Weather and Calendar Full Month widget which I both liked a lot. I have Fancy Widget (HC7 skin) and I used it to replace the Clock & Weather widget though I also like One More Clock widget's Chrome Rings Clock a lot and that's what I'm using for now and installed Accuweather widget to provide multiple city weather. If you use One More Clock widget's Chrome Rings Clock, set the Clock Update Interval to redraw every 15 seconds and Troubleshooting Options->Clock Priority to Medium to prevent time lag vs system clock without impacting battery life much. For Calendar, I use Business Calendar and I have always liked the scrollable, transparent, Agenda Widget of Business Calendar. Additionally, the S3 motion gestures (e.g. dial contacts) still work on Nova Launcher Prime. I really like being able to have 5-7 apps/widgets, with 3 pages on the Dock as well as the ease of creating folders like I had in previous Android OS/ADW Launcher Ex. Install TeslaUnread app as well for unread counts for SMS, Missed Calls, and possibly Gmail.
With regards to TW on the S3, I like it as well, especially the Full Month Calendar widget which is very readable compared to others like it. Scrolling wallpapers are nice but not that big of a deal for me and I can adapt to the way folders are created on it. The S3 and TW launcher is smooth and fast with no lag and that's the most important thing for me.