If you have to choose one of these two people to study, I suggest you study Dong Qichang. There are three reasons;
1. Dong Qichang's calligraphy is the essence of Jin and Tang books and has a strong personal aspect. Its structure, composition, use of ink, and movement of qi all have its own unique features. It makes sense for the former Qing emperors to strongly advocate learning from him. Wen Zhengming, on the other hand, has many writing styles, and his running script, regular script and cursive script follow different schools, making it confusing to learn and not the first choice for beginners. It's okay as an appreciation.
2. To study Dong Qichang, you should pay attention to his calligraphy theory. Many of them are very inspiring to those who study calligraphy.
3. The most important thing is that it depends on your interest in learning. If you like his calligraphy very much, then learn it! No matter who you learn from the classic masters of the past, it will be helpful to you. But don’t be greedy. In the process of learning, you will find that his calligraphy has many similarities with his predecessors, which will prompt you to go back to the Jin and Tang Dynasties and make you make a qualitative leap in learning.
In short, learning is a long process. Only by constantly working hand in hand and heart in hand can we improve and have fun in the process!