The Ego Twist is designed for basically 2 atomizer ranges, Low Resistance and Standard Resistance. The 1.5ohm to 2.0 ohm range is for the low voltages (3.2v and not to exceed 4v) and the 3.0 ohm which is designed to go from the 4.0 - 4.8 range. So in short, get both for different experiences.
Probably the best choice on the market right now is the Vision Vivi Nova for a couple reasons. You can rebuild them, which isn't difficult to do, and you'd save a ton of money doing it. Secondly, they come with 3 atomizer heads (that each have a higher resistance) so they are perfect for variable voltage devices. The only thing I would recommend is getting an adapter that doesn't have the cone threads on the outside, it's just the 510 adapter for the battery and that's it. The reason for this is cosmetic. The vivi nova will fit into your 510 battery threads but it will leave the cone threads exposed which looks crappy. The vivi nova itself is not a pretty device. It's as ugly as a dog, but this adapter I speak of will improve the streamline of your ego. Without it, it kind of dips in at the battery connection which makes your PV look not unlike a weird lollypop.
If you aren't ready for rebuilding your atomizers you can buy extra heads for it in any of the three resistances. They're marked on the atomizer so it's easy to keep track of which ones are your favorite.
