Benefits of Pro antivirus vs free edition?

I first used (purchased) Avast! 3-4 years ago because they had a version for Windows Home Server at that time. Since then I have used on my PC’s and several friends/family members also (a mix of Pro and free versions). I have been overall satisfied with it.
My questions is this: Is there really an advantage of using the paid Pro version vs the free version? My 3 pc Pro version expires in a couple of weeks, and I was searching for best rated antivirus products. I read a quote from Avast that said their free version uses the same “engine” or similar wording as their premium products. Any opinions?

Here is a comparison of Avast products.

http://www.avast.com/free-antivirus-download