From what I've heard, mold/mildew is a common problem with front loaders. My apartment complex has two washing machines, one top loader and one front loader. People always leave the top loader open but the front loader usually gets closed. The front loader usually smells a bit more mildewy and I've wondered if everyone closing it right after the laundry cycle is why.
Also they just started charging 50 cents extra for the front loader which is unrelated but really annoying.