From a practical point of view, it is better to practice running script, because running script is the most used in daily life. It is suggested to start with the radical first, and then practice the whole book after practicing the radical. The effect is good, but the stroke order of running script and regular script is different. It is suggested that the stroke order of a word should be clarified, and then the word should be practiced, which will get twice the result with half the effort.
But regular script is the foundation of calligraphy. If it is well written based on characters, I suggest practicing regular script again. Only by laying a good foundation can we really understand calligraphy.
Of course, from a practical point of view, you can also practice some words like imitation of Song Dynasty and Pingwei. Compared with regular script, these two kinds of calligraphy are easier to practice, easier to practice, and can also practice basic skills. More importantly, they are also commonly used.