I love Johnson & Johnson's Talc Baby Powder (the original). It works wonders for me in preventing diaper friction and in aiding in preventing diaper-rash. I am careful not to inhale it accidentally while I apply it (I squeeze or shake the container into my diapers while I'm wearing them), for it is bad for the lungs. What makes the powder work is what makes it dangerous to inhale: the shape of the mineral plates. Talc plates slide easily one over another, but they apparently lodge in the lungs and work ill there. Nonetheless, it is an essential, must-have item on my changing-table.
For me, cornstarch powder can worsen or even cause diaper-rash. Seems for some, like me, it can fuel a yeast infection, which can be one of the causes of, manifestations of, or sequelae to a diaper-rash. Cornstarch works wonders for many (Ken Kesey was a big fan, although he was not to my knowledge a diaper-fetishist), but for this adult-toddler diaperboy, the tried-and-true talcum works splendidly.
The only down-side of any baby powder is, as is well-known, interference with the proper adhesion of the tapes on disposable diapers. Even just a little powder on the fingers, the tape, or the landing-strip can spell disaster. I have had a number of seemingly well-taped 'sposies come all undone (oops!) for this very reason. Not fun. That's another reason why I prefer to squirt or shake the powder into my disposable diaper after it's actually snugly taped on.
I should add that if one mingles the scent of Johnson & Johnson's baby oil with the J&J talc powder (but not the cornstarch, which is differently scented), the result comes surprisingly close to the ever-elusive, evanescent, magical Pampers scent from the '60's and '70's. Hope that comment does not amount to a hijacking of the thread.