After using GO and Apex for the past couple days, I purchased Apex Pro. They are very close to each other and I will probably bounce back and forth between the two. I liked that upgrading to Pro on Apex gave me a set of unlocked features that were very easy to understand. Go has a whole bunch of modules that can be downloaded or not, some paid and some free. I couldn't quite figure out how much my out-of-pocket cost was going to be for the features I wanted.
I like that Apex Pro not only supports Apex themes, but GO and ADW themes as well. One thing I do not like about Apex is I cannot figure out a way to hide apps in the app drawer ; something that even stock TouchWiz does easily.