SMMs who cooperate with customers, while not working in the agency. As a rule, they are not individual entrepreneurs and cannot enter into contracts.
Freelancers often have a narrow specialization and focus on one direction - for example, targetologists or administrators of VKontakte communities often work in this format. Freelancers are both executors and managers of their services. Usually they are simultaneously engaged in several projects.
Pros: the price is often lower than that of the other two categories, the ability not to pay for sick leave (project payment), the ability to make a small order (order only part of the services or a service in a narrow niche, for example, only an avatar for the community), communication directly with the performer ...
Cons: it is difficult to control the responsibility for the project, as a rule, it is impossible to pay by bank transfer and by agreement.
SMMs who work in hiring on the client's side. They are engaged in one project, but support it comprehensively. Several specialists may work for a large company at once, but it so happens that one person is engaged in content, design, and targeted advertising.
Often, there are full-time specialists in those companies that have a lot of feedback on social networks - for example, they are accepting orders and selling through social networks (and these sales must be closed by someone) or a large amount of work with reviews and comments from subscribers. In-house specialists can work both in the office and remotely, by agreement with the customer.
Pros: responsibility for the project can be written in the KPI and in the job description, only your project is managed, they have access to the necessary internal information, they can quickly respond to changes and company news.
Cons: formal employment requires taxes, leave, sick leave, and maternity leave. You hire an employee, and you follow his work too.
Agencies, first of all, differ in that they employ not one specialist, but a whole association. Therefore, it is easier here with the distribution of responsibilities: several narrow specialists are engaged in one project.
Working with agencies is not always more expensive than working with a full-time specialist. There are, of course, top agencies that are very expensive, but the cost of working with a small agency will be slightly lower than the salary of a full-time SMM specialist in Moscow (or approximately equal to the salary in the regions). But the services of freelancers, of course, will come out much cheaper.
Pros: they work as a legal entity, there is the possibility of paying by bank transfer, they are responsible for the project under the contract, several narrow specialists work in the team: if someone is sick or quit, they themselves find a replacement.
Cons: they often do not take on small tasks, specialize in complex work, sometimes they cannot work for cash or with individuals.