One out of two options..
Either sight, apart from basically looking at things, I use more other senses to identify things and people more. I recognise people's smells and tones of voice much better compared to how I visually identify them as half the time I don't remember what people look like just usually they're eyes or a specific feature the rest is a blank slate when it comes to recalling someone's face.
Other than that.. Probably smell. But then I'd just be paranoid if I smell bad and won't know if food has gone off until I taste it....