Each businesses has a designated person who be served on behalf of the business, called a Registered Agent. When serving a business ask for the Registered Agent, determine their name, and serve them. If a Registered Agent cannot be found, it is allowed to serve a corporate officer (ie: CEO, COO, etc), owner of the company, or other individual authorized to accept is allowed.
Service upon a Registered Agent or person authorized to accept is considered Personal Service.
If you see a person named along with the business on the documents/coversheet, then this is likely the Registered Agent.
If an employee isn't sure whether they're authorized to accept service, don't serve them. It is better to make an additional attempt than a bad service.