I use Advantage drops and have for over 6 years, and have never had a problem with rashes or allergic reactions. However, I have heard some pets do have problems with the drops, and your aunt's maltese could be one. I was told by my vet that most of the flea preventative drops contain pretty much the same ingredients, but she believed that pets seemed to tolerate Advantage better, so that is what she recommends.
She also recommends waiting at least 48 hours after bathing before using the drops to allow the natural oils in their skin to return to normal in order to help spread the flea preventative over their body. It is also important to buy the correct dosage for your pet's weight. I've tried the cheaper drops from Walmart last year, and found them to be very ineffective.
I never had much luck with the flea collars, and prefer the drops. But I live in Florida, where fleas are very bad especially during the summer months.