You might find out that you are like me and need a variety of strengths. I smoked ultra light analogs. I ordered 0, 6, 12, and 18 nic level juices. In the morning, when my craving is the strongest, I use the 18. Most of the rest of the day, I vape 12. In the evening, when I am watching TV or reading and I vape for a longer period of time, I use 6 so I don't have to worry about getting a headache from too much nicotine. I keep the 0 so if I find a juice is too strong, I can dilute it with the 0 flavorless.
So far, this has worked for me. I never tried 24 and probably never will. Sometimes, the TH on the 18 is too much for me, so I'm pretty sure I would find 24 unpleasant. For the first few days, I found the sweet juices way too sweet and the only thing that kept me off analogs was either low nic tobacco juices and light vanilla/caramel juices. Everything else made me feel ill. Now that I'm used to vaping, I still use mostly vanilla/caramel based juices like KBV's OMG, but I also enjoy swedish fish, straw burst, and some of the fruit flavors, mostly in the evenings.