Which server should I use?

The program allows working with four servers.

They store historical data and run a demo server for trading on the built-in demo accounts such as ATAS sim and Crypto Sim. It also has a demo connection called Crypto data which provides quotes for crypto exchanges.

The platform does not provide online quotes for stock exchanges, therefore, you need to connect a trading account.

The list of available data providers can be found at the link below:

https://support.atas.net/en/knowledge-bases/2/articles/375-which-account-for-trading-and-quotes-better-to-choose

It does not matter which server to use because they are all the same.