38mm looks like a good fit for your wrist, but it all comes down to which is more comfortable. I have 175-180mm wrists (depending on which one and where I measure). I tried on both sizes in the store just over a year ago. At first I was struck at how close the two sizes are in person. The 38mm was not as small as I expected, and the 42mm was not as large as I expected. I tried both sizes on with several different band types and I just couldn't get the 42mm to sit comfortably on my wrist. I kept fiddling with it and adjusting the strap, but it just felt odd. When I tried the 38mm on it just felt right without any fiddling, and I thought it looked better on my wrist size.
I have never given it another thought, because I have been so happy with the 38mm size. It won't hurt to try the 42mm on in the store again. If all things are equal on the comfort and fit level, and you like how the 42mm looks on your wrist, why not have a little extra screen real-estate? On the other hand, if you are happy with the 38mm then you save enough on the next Apple Watch purchase to buy another watch band!
Sean