If you look at the Products panel on the left of the questions list, you'll see the number of questions asked that listed that product. This might give you a rough idea of the popularity of different toolboxes. Today you'll see
12,843 Image Processing
2,488 Compiler
2,423 Statistics and Machine Learning
2,254 Deep Learning
2,214 Computer Vision
So the Image Processing toolbox is far and away the most talked about toolbox, followed by Compiler, stats, deep learning, and computer vision with all about roughly the same number of posts.
