The best software development process model for a tech startup is Agile. Agile is an iterative approach that breaks down software development into small, manageable chunks called sprints. This allows developers to make quick decisions and rapidly respond to changing requirements. It also encourages continuous feedback from customers, allowing teams to adjust their plans in response to customer feedback. Agile allows organizations to move quickly, making it ideal for tech startups who need to develop innovative products in a short time frame.