The right resistance is going to vary by user...mine is generally 2.0 ohms (I like the Boges best). For some juices, I'm using a Volt X2 (3.7 v also) with 2.8 ohm cartomizers because the juice behaves better at the lower wattage. A lot of people like the 1.7 ohm cartos on the KGO...I don't particularly.
Order a range (I'd suggest trying 1.7, 2.0, 2.5, and 3.0 ohm cartos) and experiment. You probably won't like the same wattage on all juices. Watts gives you heat...on a single coil carto, wattage is a good predictor of heat that you get to vaporize the juice. Output watts on a KGO (the batteries aren't regulated, so this will vary SOME from newly charged to almost-ready to give up) are:
1.7 ohms = 8.1 watts
2.0 ohms = 6.8 watts
2.5 ohms = 5.5 watts
3.0 ohms = 4.6 watts
If you use the same style of cartos, watts are a good predictor of the vape's strength, TH, and flavor. If you compare cartos versus other things like clearomizers (top coil, bottom coil, etc.) all bets are off because there are too many other variables.
Dang...I started off trying to simplify. See how this gets?