Given the choice between using a miniature martell cognac brandy bottle and gauze (the preference of the vast majority) and smoking off foil, I definitely always choose foil.
Smoking off foil may well be a less efficient, more wasteful way of taking crack, but it's by far a cleaner hit. After smoking off gauze for a while my lungs felt burnt out and I constantly coughed up bits of wire. Not pleasant and definitely not good for your lungs. So I swooped to smoking it off foil, like heroin. I also think off foil, I get a stronger and more concentrated hit... I prefer an intense big hit in one rather than several smaller hits.