If you are talking about cartomizers, I'm happy in the 2.8-3.0 range, although 3.0-3.2 works too. For lower resistance, I generally use the dual coils at 1.6 ohm. But I can only use those (DCCs) on my 3.7 devices, on 5v (which I use often) I go with the higher 2.5-3.2 ... sweet spot falls about 2.8