Hypertherm Powermax Voltage Divider, Preference for THAD-10

Which voltage divider setting is prefferred for a Hypertherm Powermax plasma cutter when connected to a Mesa THAD-10?
The options are 20:1 _ 21.1:1 _ 30:1 _ 40:1 _ 50:1
Is one preferred over the other for better resolution or response time?
 

50:1 worked well you can use the THCAD10 without any modification, 
Some good practices are:
-Place THCAD10 as close as possible to the Plasma power supply.
-Use a shield cable and connect the shield to GND on one side only.
-Use a ferrite bead on the control side to reduce induced noise 
 

It depends on your machine amperage. No scaling resistors are rwquired. Most people use 20:1 which gives a 200 volt full scale, 125 amps might be better at 30:1. (300 volts)
The thing is that the THCAD is rated for overvoltage of 500 volts. The voltage will only go over 200 volts on piercing when we do not care about the voltage then. During cutting voltage is between 100-170 volts. Keeping the max voltage range low means the readings are more accurate as more of the ADC's range is used. 50:1 is popular with a lot of non-linuxcnc THC's  (probably with a 0-5 volt ADC). That would be better for a THCAD5.

I Agree with you regarding the Optimisation of the dynamic range (headroom) of the AD converter.
will double check all the machines most of them are hyperterm 85, 105,125 and maxpro 250.
so I need to check max voltage and select the proper divide ratio

Thanks for the input!
I used 20:1 on the Hypertherm Powermax 85 and F/32 on the THAD-10.
I switched from 50:1 and F/1 settings, but I did not notice any substantial difference.
I just finally updated my CNC Plasma table from PlasmaC to QtPlasmaC.
It's been on the to do list for a very long time and I finally got it done. So far I like the update, sometimes it pays to stop, and "sharpen the axe"!
My Hypertherm Powermax 85 had been giving a service code and needed repair. It took a replacement main circuit board.
Hypertherm plasma cutters have served me well. I have been using this one for a lot of cutting since 2014.