Quark.
At first, he's presented as someone who would cross almost any ethical boundary to make a deal (e.g., the man a ran a business for the Cardassians when Terok Nor was basically a concentration camp).
And the more you learn about him, the more you realize that some of his insecurities about being a "good Ferengi" comes from the fact that he does have a moral center. That he's willing to take risks beyond the Rules of Acquisition to help people, including when he was running a black market to get food to the Bajoran slaves.
I also thought part of what makes Quark's commentary on humanity so incisive and thought-provoking is that it doesn't come from ignorance. When he confronts Sisko, about Sisko's bias against the Ferengi, he mentions human slavery and Nazi concentration camps. That means Quark went through the trouble of actually researching human history, and his skepticism of Federation values doesn't come from discrimination based in ignorance, but a fear based in human history.