Once the shirt material has been examined, the next place to look is the shirt collar. Indeed, there are some haberdashers who would suggest that this might be the first place to look, since the collar is all one ever sees of the shirt, that and perhaps one-half inch of cuff. In many respects, the shirt collar plays a role similar to that of the silhouette of the suit. It sets the tone of one's dressing style and is probably the key to the shirt's longevity. Perhaps the most important aspect to consider is the relationship of the shirt collar to one's own physical proportions.
Proper balance is the ideal.
If a man is large, with a broad face and bullish neck, nothing will appear sillier under his chin than a tiny collar - rounded, spread, or otherwise. Generally speaking, the larger the man, the larger the collar he can take. But one oughtn't push this notion too far. The proportions of the shirt collar can either draw attention to a man's physical irregularities or de-emphasize them, which is generally the more flattering course to follow. Therefore, if you have a short neck, look for shirt collars that lie flat.