To choose the best server location, firstly, you have to get your brokers MT4 IP, this is a few guide:
Guide to get the IP:
1. Open your MT4 platform
2. Make sure it connected to the server
3. Click on File , then look for Open Data Folder and click it
4. Find a Config folder, then open it
5. Open the file with extension *.srv with notepad
6. Inside that file, you'll find your server IP
Guide to check latency:
1. After you get the IP, you may visit our looking glass page at https://winnervps.com/looking-glass.php
2. Choose one of available server location, and type your MT4 server IP without the ports at Network Tests section
3. After you type your MT4 server IP, you can run the test, and find the result
4. Repeat this process with other server location, compare the result, which is the best latency that suits you