Assuming you are talking about whether men should wear tight or loose fitting undershirts, it really depends on the situation and personal preference. If you are wearing a dress shirt and tie, a tight fitting undershirt will help create a smooth look. If you are going for a more relaxed look, or if your build is such that tight shirts are uncomfortable, then a loose fitting undershirt might be better. Ultimately it is up to you and what makes you feel most comfortable.