I was a heavy smoker and rolled my own for years and when I started vaping I thought I'd better go for the strongest e-liquid I could find locally, which was 24mg. I got myself off the cigs, which involved a lot less drama than I was expecting, I was very pleasantly surprised. When I'm having an occasional lazy day at home, I tend to chain vape and using the little ego/CE4 device I had at the time, 24mg posed no problems for me. As Lessifer said above, a lot depends on the gear you are using, I wouldn't consider using 24mg in a dripper for example. After a while, I went to stock up on some e-liquid one day and they had ran out of all the 24mg's, so I picked up some 18 instead, but I remember at the time being a bit worried about feeling extra cravings or some sort of withdrawal because I was dropping nic levels (still quite new to vaping at this point) and I didn't feel any difference in the vape at all. That started me off on the path of slowly lowering my nic levels, which is now down to 6mg. Having said all this, everyone has different gear and their sensitivity to the substances in our e-liquids varies so what works for me might not work for someone else