What is the best way to organize file access (FTP, SMB or RDP)?

Question

Access rights

Hello!
Given:
A server running Windows Server 2012 r2 and 5 client PCs connected by a local network without Internet access.
The domain is raised on the server, AD user accounts are created. The main and only task that should be performed in this LAN is the creation by users of documents in the MS Office package and their centralized storage on the server, and there must be a strict differentiation of access to resources - no one except the author can get access to his files. Third-party USB, HDD, FDD, CD / DVD drives are not allowed to be connected.
Question:
What is the best way to organize user access to files stored on the server:
1) Access via FTP server;
2) Sharing folders (network drives);
3) Work of users through RDP?
Which of the options is better in terms of the security of protected files?
Thanks in advance for your comments!

Answer 1

Provided that client PCs are added to the domain, the option with correctly shared folders on the server (with correctly set permissions) is preferable in my opinion.
With advanced security requirements, it is also a good idea to implement EFS and smart cards.

Answer 2

Folder sharing of course. Create security groups for each folder. You can also implement EFS and Bitlocker. RDP purely for shared folders is somehow not serious, unless these five computers are on the same local network as the server.