I agree that they are pretty much the same, but North has a few more Premium stores. If you are not shopping at any of the higher end stores, they parking and traffic was much better at the South outlet when you were there recently.
FYI for the OP - most of the parking at North are at a couple of multi-level garages. South is a typical spread out ground level parking lot. I was at North last Black Friday during the late morning. Finding parking wasn't that bad - it was actually pretty easy. I just had to drive up the garage. Closer to home I've ended up circling around looking for a parking spot just waiting for someone to leave.
Here's South:
https://maps.google.com/maps?q=las+...near=Las+Vegas,+Clark+County,+Nevada&t=h&z=16
And North:
https://maps.google.com/maps?q=las+...&hq=las+vegas+outlets+north&radius=15000&z=16
South is like a long, thin rectangle. It's basically one building, but with some add-ons (the Google Maps satellite map shows those parts under construction). Then there's the annex in the SW corner.
North is more of a modern airy outdoor outlet mall. The body of the mall seems like a lot of the newer upscale outdoor outlet malls I've been to, such as the new one in Livermore, California, the one south of Portland, Oregon, the Outlets at Orange in Orange, California, or in Tukwila, Washington.
If I could only choose one and it's not 100 degrees outside, I'd go to North. However, check the list of stores since they're not the same.
It was also a bit bizarre, as I saw a lot of people shopping along with luggage. A lot of shoppers were just dropped off there by taxi with their luggage in tow. They must have either just arrived and it was too early to check into a hotel, or they had checked out and wanted their luggage with them before taking a taxi to the airport.