Here's my take on the replacement coils:
They come in a few different resistances, 1.8, 2.4, 2.8, 3.2, and 4.0 ohms. A week later and the 3.2 ohm one I started with is still working great. I've come to find that using it at 4.8 v is not too much for me but that's as high as I would go with that one. As for the 1.8 ohmes one, I set either my twist c or my ProVari at 3.2 and It works great at that voltage.
For a regular eGo I would suggest either the 1.8 or 2.4 ohmes.
For kgo or other 3.7v - 4v batteries I would suggest 2.4 or 2.8 ohms.
For 5v or 6v mods you would probably would want to use 4.o ohms.
If you have a variable volt mod or twist c any of these will work for you.
The lower the resistance the warmer the vapor and increased vapor production just don't over do it!
If I had a true 3.7v device I think the 1.8ohm one might be too warm for me, just like if I had a true 5.v mod the 3.2 ohm one would be pushing it also.