When it comes to his shirt, every man prefers a different kind of fit. There are the main blocks; slim, tailored, classic, traditional. Different shirt-makers may have a different name for one or two, but they correspond roughly to these blocks. Beyond the main blocks, there are the more individualized preferences men have which manifest in custom tweaks and exact measurement requirements for bicep width, chest, waist, length etc...
I don't think there is one right, or wrong fit. It's so individual. To think there is a right or wrong is simple minded, to put it bluntly and crudely. Men have different body types, images of what they want to be and who they want people to see. It seems to me that for every man there is a different preferred fit. Every man has a different fit which will feel natural, and perfect. Every man has an individual idea of who they are, who they want to be, and who they want people to see.
I am a man of the traditional fit. I could list every specific measurement I want to see in a shirt but it would become pretty boring for most. To put it concisely, I prefer my shirts to appear as close to the 1960s Brooks Brothers OCBD fit as possible. Full chest, arms and waist and long so that there is never any concern of unintentional un-tucking occurring. When I have a shirt made custom, I have little tweaks here and there which result in a shirt which is obviously not the exact same as the 1960s fit I mentioned. But, the general orbit / look I am always in, is this classic traditional fit. This traditional fit is the image, the shirt, that the custom measurements I have developed for myself are always pointing toward.
For many men today, the traditional fit is too roomy. They prefer their fit to be snug. They don't want their shirt to feel big and full. Maybe they only rarely wear sport coats and so their shirt is their outer layer of clothing, and they want that outer layer to be snug, or at least not too full. That's great, all men have their own preference. It isn't right or wrong, it's preference. They probably hate the way the traditional fit looks, and think it's too roomy, too big. For me, the traditional fit is perfect in every way. It is truly my ideal. Under a blazer or sport coat, it's perfect. I love the feeling, and classic mid century casual aesthetic it creates when worn without a blazer or sport coat, with my shirt as the outer layer. Untucked with the long tail, a shirt not made to be worn untucked, with 2 buttons unbuttoned, wearing jeans at home on the weekend, this is it's own perfect setting as well.
Everybody has their own aesthetic, personal style and personal approach. Some people have very specific wants, and some more general preferences. My shirts are my most specific, curated and individually tweaked article of clothing. My specific wants and preferences are unique. I have, over time, developed my perfect measurements for every aspect of the shirt. These measurements help create the perfect shirt for me, my unique personal style, aesthetic and approach.
I love the natural waves and ripples that appear in an OCBD cut in a traditional fit. The ripples in the fabric over the chest when sitting, the folds and crinkles in the arms when standing with hands in pockets, the extra fabric that bows in the back when tucked in. All of this is a part of this traditional aesthetic. This is the aesthetic I am always approaching and that which feels most organic.