As I have said before, this decision depends on your wrist size, nothing else. If a 42mm fills the entire width of your wrist, it won't look right, like on me.
I have a 38mm because a 42mm looked ridiculous, and pretty much looked like I had a large screen on my wrist rather than a smart watch.

I have a 38mm because a 42mm looked ridiculous, and pretty much looked like I had a large screen on my wrist rather than a smart watch.