I purchased both touring plans for the trip I just returned from. I used both to construct my touring plan. Here's my take:
Touringplans.com is good for someone who just wants to connect the dots. Go to attraction A, then B, then C. This was good during my initial stages of planning.
TGM explains WHY you are doing what you do. This approach requires a better understanding of what you are doing. TGM allows you to think on your feet and allows you to navigate around unexpected events.
For example: When we toured AK, it was advised in the plans to get to the Safari right away. When we arrived at the park, that attraction would not be open for 45 minutes after opening. Neither plan provided what to do in this situation. However, with TGM, I was able to think on the fly on what I would do and why I was doing it. If I only had touringplans.com, my assumption would have been to go to attraction B, which may not be the best route.
TGM allows you to see the big picture. This enables you to handle unexpected events, which almost always occur.