Depending on what you would like to achieve, I prefer Master/Slave protocol, where you have one Master and the rest of devices are Slaves, but there are some other options.
Some suggestions you can find here: https://www.allaboutcircuits.com/vol_4/chpt_14/6.html
Regards,
IanP
I suggest MODBUS because iI worked with it, and do all you need,modbus is master slave and open protocol.see www.modbus.org for its specification.
There are many industerial systems that support modbus and there are many softwares for test modbus devices ,S7 PLCs also support modbus(they have modbus lib )