Technical what's the best ignition coil to buy? or does it make any difference?

Get mine off ebay. No brand. Just get one to suit your circuit. I treat them as consumables

3 ohm 12v no balast
1.5 ohm 6v or 12v with balast
.6 ohm, electronic ignition

Just make sure the polarity is correct

 

I will chime in with the fact you are measuring a very low resistance, put your meter leads together with the meter set at the lowest ohm resistance setting and see if it reads "0" or not. I have three meters and they all read something other than zero when I do this, I suspect the extra resistance is in the leads. One reads 0.6 ohms when I do this, that value would need to be subtracted from the coil or resistor reading at room temperature. Heat will change the value of the readings as well. Just my two cents. Mark

 

Regular multimeters do indeed have issues when measuring small resistances due to resistance in the meter wires and other factors. The only really good way to measure below, say, one ohm is a four wire measurement, where the testing current and the voltage drop sensing is done through different wires, removing any error due to wire resistance.

There are instruments that uses this method, but you can easily improvise it well enough to get measurements in the milliohm range. You just need something to send a suitable current through the device under test (DUT), perhaps a battery and a light bulb to limit the current, you need to know what that current is, and you need a volt meter to measure the voltage drop across the DUT.
Then ohms law easily calculates the resistance, if the current is 1A (for easy math) and the voltage is 0.7 millivolts (0.0007V) the resistance is 0.0007/1=0.0007 ohm = 0.7 milliohm. This way one or two (if you want one permanently measuring the current to be sure) cheap multimeters can measure very small resistances way more accurate than even many expensive multimeters. On the other hand, a proper 4 wire meter would be better and more accurate, if you really need to measure like this often.

 

I picked up an NOS made in usa accel coil