I have like a 160mm wrist.
I tried the 38mm for two weeks and thought it was fairly small compared to my previous iPod Nano watch.
Then my 42mm finally came in and I was much happier. Sure, it has that more apparent techie look and people notice it more, but I like it.
I think the band makes a big difference too. My WSB makes it look big on my wrist since the band tapers to a thinner size very quickly. But the link band tapers slower and makes the whole package look fitting!
PS: watches, historically, should be worn below the wrist knuckle (away from the hand, toward the elbow). But again, I guess that's preferential.