What should I use, Apache or Nginx?

To answer on this question, you need to parse them separately.

Apache - was created in 1995, already in 1996 it was the most popular in the world. The main advantages are strong documentation and integration with a host, more  flexibility, reliability, power and wide prevalence. One of the main drawbacks in Apache is the lack of a graphical user interface for configuration, and configuration files must be edited manually.

Nginx - released in 2004. It’s designed to support 10,000 simultaneous connections, with which it manages. The advantages of Nginx include: easy placement with minimal characteristics and performance on it, simplicity, speed and fault durability. The big minus in Nginx is the lack of built-in PHP, it can be fixed using a PHP connection through a special FastCGI interface (a separate client-server protocol).

What are the main differences between thease web servers?

Apache uses a branched multi-threaded solution, in other words, it communicates with each client individually. Nginx does the same, it uses a nonblocking event loop, if it is easier, then it unites users who work asynchronously.

Why we use Nginx?

Since our hosting is designed to support professional sites, the speed of loading the site and its stability under heavy load is important to us. And Nginx creates one thread, and immediately processes it, without creating unnecessary processes. Because the load on the servers is not so great. The less the load on the server will be lower, the more it will stands.