For a fixed voltage eGo battery you can run any of the replacement coils, I would stay between 1.8 - 2.2 but it all depends on what you are looking for. 2.2 is a good mid-range coil for most juices. I make my own coils and target 1.9 - 2.0 ohms and they produce good vaper and taste on the fixed voltage battery I have. They are also good on my variable voltage / variable wattage devices.
I just started trying micro coils in the t3 @ 2.4 but that will confuse you more.