The choice of software development model is influenced by the complexity and size of a project. For smaller and less complex projects, agile methodologies such as Scrum or Kanban are often preferred. These methodologies emphasize flexibility, collaboration, and iterative development to quickly deliver value. On the other hand, for larger and more complex projects, a sequential or waterfall model may be suitable. This model involves a linear and structured approach with distinct phases like requirement gathering, design, development, testing, and deployment. The choice of model depends on factors like project requirements, team expertise, stakeholder involvement, and budget constraints.