5 applications between Raspberry Pi in a project I did. 1 "Server will be Client to 4 of them. Will there be more traffic from the tool here, or via TCP/IP or using MQTT? Which is more detailed? Can you help? Good work...
The priority and important part for the situation you specify is the delay.
If communication is large data streams instead of multiple, TCP should generally be preferred. By agreeing with the previous comment, it would be quite appropriate to use MQTT if the code complexity is aimed to be minimized.