i ordered 5 bottles of the same flavor (hazelnut) from the same vendor (Vixen Vapors) all 60VG/40PG with nicotine levels from 0-24mg. first thing i noticed, the more nicotine the darker the liquid. the 0mg was crystal clear, the 24mg dark amber. I filled 5 different cartos with each liquid, and i really couldn't taste any difference. there was a huge difference in the
throat hit. the 0mg was like
vaping 100% VG, just straight air. the 24mg was pretty intense. i've tried a variety of liquids in the 30-36mg and found them to harsh for me and i still smoke a few ryo analogs everyday. overall i found i prefer 12-16mg depending on the flavor.
I tried all of these on an apollo vtube at 4.5v on boge sc 3.0 ohm cartos. hope this helps.