I for one would have to vote for the under the tit rash. The sh*t hurts. At least with thigh rub you can sit down and chill or desperately find some relieving A&D ointment or some baby powder. I know this is a disturbing topic but I'm curious.
If you are having bad rashes like that it might be worth going to get tested for diabetes. my mother used to get those all the time a nd then she found out she was diabetic. i personally use the before mentioned deodorant trick or desitine. works wonders!!! my legs don't really rub that much together but then again i always wear jeans or pants of some sort.
I've also found wearing "bike shorts" (ie, short leggings made from a cotton/lyrca blend, not the ones that real cyclists wear) under my skirt or dress works brilliantly to prevent the thigh rub thing.
For all who suffer from the pain of rashes in crevices, due to skin surface yeast. Heres a tip, purchase miconizole shampoo from your Veterinarian. brand name DVM Malaseb shampoo. This is a soapless shampoo. Shower with it as soap during those ourbreaks and the problem will reslove,quickly and with this stinging pain. And watch your carb intake, carbs break down to sugars and yeast love sugar. Be well and happy.