Fuel Gauge OHM question

I am currently researching new gauges and my question is, what is the decideing factor on what OHM to purchase?
The options are as follows:
0-90
73-10
240-33
Or a programmable unit = Pretty damn salty

I'm guessing it has to do with what sending unit is used, if so how do you tell what you have for a sending unit.

Syphon all the fuel out of the tank, get a reading at the sender in Ohms, fill the tank up and get another reading. Or pull the sending unit and play with the float. Mine was 60 empty and 7 full.

Terry