Best controll board for LinuxCNC

Which controller board is best to use with LinuxCNC? I have a 3-axis router. DM542 stepper drivers and Nema 23HS9430B motors

If you can justify it, Mesa 7i96S.
For very cheap use an old PC with a parallel port, or a new-ish PC with a parallel port add on card.
Both versions are extremely reliable, proven by many machines in daily use.
Depending on requirements, parallel port might limit the maximum speed, still very usable always.

The 7i96s is a drop in kind of replacement.
At the risk of adding far more complexity, you could consider Ethercat. There are some interesting options emerging. eg The Lichuan 4 axis stepper driver in a single package. I only hope I can get this going, Also available in closed loop. At USD $92 plus shipping, it competes on price depending where you live.

 
 

As I understood open loop drivers and motors are existing and are kept in the system. (for the time beeing)

It is probably difficult to answer the question. What makes a controller better (best)?

• cheap? (two parallel ports (PCIe cards) in old office PC)
• least amount of re-wiring? (existing parallel port machine?)
• cheaper? (but not a bit of documentation) ( FPGA cards of unknown origin)
• Is wasted time cheaper than money spent?
• easy to set up? ( pnc config)
• upgradable? (linear scales, tool changer, rigid tapping, closed loop positioning, linear motors)
  
  I used an old parallel port machine, changing form mach3 to LinuxCNC was 90% figuring the "charge pump" out (no re-wiring, all in software), then the computer quit service and the replacement had no parallel port. (a 10$ PCIe card fixed that). 
  Having problems to get an encoder running a Mesa card (6i25 with daughter card) went into the machine. (solving the spindle encoder issue)   (it still is a Frankenstein mixed Mesa and Parallel port). 
  
  Greetings Timo 
  
  p.s. the UC300ETH is that working with linuxcnc? Some older threads stated it does not work.
  forum.linuxcnc.org/27-driver-boards/2982...moothstepper-to-mesa