Ethernet for everything. The ones posted are to compactlogix 1769-l32e. The VFDs are Altivar 71. Which are controlled over ethernet also. The next setup on my list is with a Proface and a compactlogix 1769-l30er.
I was curious because I was recently involved in a project that used 2 of those Proface HMIs connected to a Beckhoff CX controller over Ethernet. We had a terrible time getting them to connect. After about 2 months, the first one flaked out and refused to connect anymore, so it was pulled out and replaced with a different HMI. Then a few months later the 2nd one did the same thing, so it was pulled out and replaced also.
What model where you using the ones I showed where modular type with the 22mm knockout. I have not had any issues like that so far. A lot of our setups have 2 HMI's talking to one PLC with no problems.
It looked exactly like the one you have in the picture. I think the problem was in their ADS driver that is used with Beckhoff TwinCAT. I wasn't able to fully narrow down the problem because the line was down and after a couple hours of trying everything we had to do whatever was necessary to get things back running.
These are GE Fanuc Proficy View Runtime. I have these on a View Runtime server and can be accessed through a web Browser with Java. I have a couple stand alone HMI with GE Quickpanel.I wanted to try Archies Advanced HMI but haven't had the time and there isn't a GE SRTP Driver. (GE Version of Ethernet.)I could try the Modbus but it gets complicated