Is my worker a Contractor or an Employee?

We don't get to decide!  Like all things in Business Compliance, the IRS sets the rules and it is up to the Employer to follow them. You must classify your worker per set guidelines.

(Note this 1099 or W-2 Employee Calculator: Not sure if a worker is a contractor or an employee? Just answer a few simple questions here https://quickbooks.intuit.com/r/1099-w2-employee-calculator/ )

 The most comprehensive information on making this determination comes directly from the IRS publication Understanding Employee vs. Contractor Designation. The brief summary is:

• Do you have Behavioral Control?  The behavioral control test focuses on whether the company controls or has the right to control what the worker does and how the job is done. Behavioral control factors include types of instruction given, degree of instruction, evaluation systems, and training
• Do you have Financial Control? The financial control test looks at who controls the economics of the worker’s job. Being able to work for multiple employers and providing one’s own tools may indicate Contractor status. Factors pointing to employee status are eligibility for reimbursement of travel costs and payment based on hours worked. The financial control factors are significant investment, unreimbursed expenses, opportunity for profit or loss, availability of the services to the market, and method of payment
• What is the Relationship? The relationship control test examines how the parties perceive each other. Providing paid vacation and retirement benefits indicates a worker is an employee, as does hiring to provide services indefinitely rather than for a specific time period. Written language stating the worker is a Contractor is not determinative. The factors include the existence of written contracts, offering of employee benefits, permanency of the relationship, and services provided as a key activity of the business

Employers must weigh all of the above factors when determining whether a worker is an Employee or a Contractor. The key is to look at the entire relationship, consider the degree or extent of the right to direct and control. 

More "light" reading is available here https://www.cpajournal.com/2019/02/11/employee-versus-independent-contractor

See also 1099 Contractors Explained
See also Singletrack's W-9 Compliance and 1099 Filing service
See also Gusto Payroll