If you are a beginner, then I suggest according to your interest. You can find two copybooks and collect excellent regular script inscriptions of past dynasties; An excellent collection of inscriptions in past dynasties. See which font you like, and then practice. Because calligraphy depends on persistence, you don't even like the fonts you practice. How can you persist?
In terms of your future development, learning running script and cursive script have their own advantages and disadvantages, and there is no difference between good and bad. Since you are a beginner, I won't say much about some theories. In addition, when practicing, you must read more and compare more to better understand the font.
After reading other friends' answers, I'll add some.
Most of my friends think it is better to start with regular script, which is indeed the mainstream of learning calligraphy now, including me, and it is also the cursive script from regular script to now.
But according to my own experience over the years, in fact, they really have their own advantages and disadvantages. Generally speaking, starting from regular script, it is easy to copy mechanically; It is easy to write frivolous words when you are a subordinate. Of course, this is relative. It is easier to learn the calligraphy of Mi Fei, Huang Tingjian and Su Shi. Starting with regular script, it is easier to learn the calligraphy of Erwang and Huai Su. Of course, this is relative. Regular script is too standard and strict, and it really exercises the brushwork, but it will not be easy to break this rule in the future. Therefore, from ancient times to the present, great calligraphers have actually studied and achieved certain accomplishments.