Well, between ethanol and iso I would say its personal preference, they serve the same purpose and whatever you're comfortable with. For me, I know enough to know that While iso is harmful if drank (although I've know bad alcoholics that in a pinch will drink it and kill their organs in the process) I've worked with some of the deadliest chemicals on the planet (vx nerve agent and the like) that the extremely small possibility that there might be a few nano grams of iso that doesnt evorpate off the pipe after a day of rest is so slim that it doesnt concern me in the slightest since the air itself has more harmful chemicals in it (and tobacco smoke itself). I still stand by my statement about denatured alcohol tho. Not so much about the concern of the methanol (that would evaporate just as quickly as the iso and ethanol) but unless you know for certain what they put into it to denature it its rolling the dice for sure. If it was JUST methylated, then that's fine. But get that bitter compound or everything else they toss in there and its game over. Your pipe would quickly be ruined.