Originally Posted by Mark Anthony
I feel proportion to your wrist and overall size (height/weight) etc. is key. Then you need to look at thickness and overall styling as some 42mm watches look a hell of a lot bigger than others.
+1. Although it's rare for a small watch to wear big, some big watches wear small, especially if they're thin.
For dress watches 36-39 will be a range that will probably be safe regardless the trends and for casual 38-42.
Interestingly, when wristwatches first came in to existence they were essentially pocket watches put onto straps so the diameter was larger, say 40-45mm. Then come the 40s they got smaller and purists tend to associate the 50s and 60s as the quintessential period of what watches should be like. Then early 90s they grew again and now it appears some makers are slightly downsizing again.(JLC, Lange, Patek).
That's why people calling it a "trend" amuses me. Big wristwatches have existed for as long as wristwatches have existed. If anything is a "trend," it's that they became increasingly smaller. Now people are coming back around to big. Sort of like cell phones--it used to be the smaller, the better. Now people are asking for bigger iPhones and using mini tablets (e.g., Galaxy S3) as their phones. Is that a trend toward big? Not really; cell phones started out big and got smaller. People are just appreciating larger form factors again.
I have watches ranging from 36mm to 46mm. Each has its place.