Service uniforms see the most ubiquitous use in Starfleet. Designed to be both presentable and comfortable, they are ideal for most operational starship and starbase duty. Officers on bridge watch, administrators in a starbase and researchers in a lab all might wear service uniforms.
Service uniforms are considered "business" or "business casual" dress and officers typically will be wearing these. Since most officers in Starfleet work in a clean, office environment, the service uniform is appropriate attire most of the time.