Being emotional and expressive aren't quite the same thing. You could say a lot of the Links are rather passionate about what it is they set out to do, they do have motive or drive to conquer their challenges in the name of something they hold dear, but stoicism doesn't nullify that underlying passion. I don't express myself much in person, but that doesn't mean I'm apathetic or unemotional.
But you can also say that just because Link has reactions to things, doesn't mean it's directly tied to emotion. Most people would react to being hugged by a redead with disgust, and that doesn't necessarily mean it's an emotional response so much as a "what the ****, get off me." Expressiveness can mean other things. Link running out of stamina and being a drama queen isn't an emotion, that's just him being an idiot.
But for expressiveness, how much Link's actually conveying what may be going on in his head, I'd say the Wind Waker and Skyward Sword Links are the most transparent about those feelings in their facial expressions and body language and stuff.