Confused and puzzled are the closest in similar meaning, as well as bemused, although that is rarely used in daily conversation. Baffled, bewildered, and perplexed are all closer in meaning too. I have never really heard anyone use nonplussed, mainly because it is actually more of a reaction-less reaction to something, if you catch my drift. Nonplussed is better used in writing, along with bewildered, bemused, and perplexed. They are more complicated versions, and although they make you sound more educated when you speak, it is easy to use them in the wrong context, and it doesn't bring your point across the same way the straightforward words like confused and puzzled do in daily conversation. As for differences, they all are kind of similar, but as I said before, nonplussed is more of a reaction to a confusing situation, which often involves someone have a lack of a reaction due to their confusion. Baffled is in line with confused, but also with bemused, and I often use it if I am referring to something someone has said that seems almost so idiotic that there is no appropriate response. I think that's all. Hope it helped! Cheers :)

They are not at all synonomous -- especially bemused and nonplussed, which have little to do with confusion. I would say that the ones used commonly in speech are #1 - confused, and #2 puzzled (other people are likely to have other opinions!)

Perplexed baffled puzzled confused for conversing and others in literature.