I have a few different types in my BOB ranging from steel wool & 9v battery, dryer lint & wax, different synthetic store-bought products, cotton balls & vaseline, etc. I keep these in water tight containers and have different types for differing conditions. I've never tried SOS pads.
As far as plain cotton is concerned, if you fluff up and ignite a standard cotton ball it will burn for about 15 seconds at the most but it won't burn very well, hence the wax and vaseline tricks. That said, a bag of cotton balls is lightweight, can be used to start fires, and can serve many other purposes in a survival situation.