I use the premium versions of both Training Peaks and Today’s Plan, so my comparison will be for the premium accounts. I prefer Today’s Plan, as explained below, but it is not for everyone- or even necessary for athletes who are just starting to get into data analysis of workouts, etc.
I like Today’s Plan better because it has more ways to slice and compare data. Hey, I am a Coach and I like to nerd out on as much data as possible. It is much more detailed than Training Peaks. To give you an example, I can add lines to the graph of a given workout showing the different target powers. The Dashboard has lots of graphs comparing PRs, training zones, HR averages, etc month by month or year by year. The list goes on, but you get the idea.
Training Peaks does not have the same detailing features as Today’s Plan, but it has sufficient information for those who don’t like or don’t need to get deep into the numbers and graphs. It is more intuitive to use and the app is way better than Today’s Plan’s app. I typically recommend that my athletes get Training Peaks until they get so much into it that they want to spend more time analyzing their data.
Hope this helps.