That's a big pile of "it depends."
Since you have a fixed voltage battery you can't adjust anything to suit the resistance of the coil. That, and different liquids produce better (or worse) flavor depending on that combination of coil resistance and battery voltage. In your case you can change the resistance of the coil but can't change the voltage. What that leaves you with is: the lower resistance you choose the hotter the coil gets. And faster. With Kanger BCC stuff that doesn't always turn out to be a good idea.
In my experience I prefer the 2.2 ohm coils. Even the 1.8 ohm coils can get too hot at 3.2 volts on a variable battery. But as I said "it depends" - on your liquids, what you like etc. You best bet would be to pick up some single coils at 2.2, 1.8 and even 2.5 ohm to sort this out.
If you are wondering what you are using now, real Kanger coils have the resistance stamped into them - on the smooth cylindrical section below that flat metal washer. You will need strong light, a bit of rotating back and forth, and possibly a magnifying glass to read it.