Hi,
there is almost a bewildering array of choices for a motion controller. To try to slim down the list I'm going to exclude anything Chinese on the
basis they don't support their customers. I'm also going to include only devices that have Mach3 AND Mach4 plugins, it means you could use either.
https://warp9td.com/ The ESS is the model of choice, ethernet connected for minimum latency Mach3 and Mach4 ready.
https://www.poscope.com/product/pokeys57cnc/ The 57CNC is the model of choice, complete, flexible and competitively priced.
https://www.cncdrive.com/ The UC300 is the model of choice, five ports worth of IO, note the Mach4 plugin is new and not as developed as others in this list, excellent record with Mach3
http://www.vitalsystem.com/portal/index.php The HiCon is the model of choice. The Mach4 plugin is the best developed of all in this list, also the most expensive especially with addons
https://www.pmdx.com/ The PMDX-422 is the model of coice but for Mach4 only.
https://en.cs-lab.eu/ Has a good reputation with Mach3 but patchy with Mach4, this company has gone off the boil when it comes to support, expensive.
All of these devices, with the exception as noted, are superb quality and backup. I personally use the ESS but would be happy with any of these units.
Craig