What is the right way, from the point of view of SEO, to make a division by city?

Question

Search Engine Optimization

Good afternoon!
How to make a division by city from the point of view of SEO?
Option 1: msc.host.ru
Option 2: moscow.host.ru
Option 3: host.ru/moscow
Please clarify the position.
The site is a directory of specialists. Naturally, each person can only work in one city.

Answer 1

msc.host.ru

The name is short and clear, compared to the second option.
Most of the popular regional directories use just such a division by city.
With option 3, you are tormented then to set redirects (when necessary) or to do human CNC.